It has been a grueling few months for Matthew Perry. Saturdays through Wednesdays he has concentrated on Servicing Sara, the romantic comedy he has been shooting in New York City and Dallas since December with costar Elizabeth Hurley. Thursdays and Fridays he has been back in L.A. taping Friends. On Feb. 16, as the hit sitcom's cast and crew headed into its most recent break, Perry flew to Dallas to resume work on his film. Then came the shocker. About a week later, without any warning, he failed to show up for work. "Following the advice of his doctors," his publicist Lisa Kasteler cryptically explained, "Matthew Perry has entered an undisclosed rehabilitation hospital."

Though the precise nature of Perry's problem remains a closely guarded secret, Kasteler concedes he is being treated for an unspecified "addiction." Perry, 31, who admitted in 1997 to an earlier addiction to painkillers, has throughout this season been attended on the Friends set by a male sobriety coach, whose presence helped convince cast and crew that the star had his dependencies under control. With just four episodes of the seventh season left to tape, May sweeps in the offing and the marriage of Perry's character, Chandler Bing, to Courteney Cox Arquette's Monica Geller hanging in the balance, NBC insiders and many of the Friends cast and crew were reportedly stunned by his return to rehab. "I've been on the set and he looks great and he's been a real trouper through February sweeps," says an NBC source. "It caught me by surprise."

Someone who works on the Friends set says, "I would guess Matthew is embarrassed that he has let his castmates down. They have the competition against Survivor, and this is an added complication. I know they're all concerned for Matthew, but no one knows when he's coming back."

Another staffer insists gamely that Perry's absence won't pose an insurmountable problem. "They'll shoot around it," he says. "They'll deal with it. It's not going to affect the show."

Over at Bright/Kauffman/Crane, the company that produces the show, an official vows, "We will still be in production and we will still have original episodes." Yet Friends writers must brace for the dicey possibility that Chandler Bing has gone AWOL for the rest of the season. If so, what's to become of Monica's season-long wedding plans? "It's all going to depend on when he comes back to us," says an NBC source. "Basically it's one day at a time."

The mood is far gloomier on the set of Paramount's Servicing Sara, where one prominent insider says, "We're still in shock trying to know what to make of it." On Feb. 24 the film's producers received work that Perry was being admitted to rehab under doctor's orders, with no date set for his release. "We have been told nothing about when he can come back to work," says a source on the set. "We know nothing." With just nine days left on the shooting calender, production has come to a near standstill. Several people associated with the production insist that the halt is only temporary, pending Perry's return. "Matthew's in every scene," says a source close to the film. "There's not much that can be done without him."

Meanwhile, true to their all-for-one spirit, Perry's Friends castmates have offered no comment and kept their own counsel. When the group sat down on Feb. 27 for their weekly reading of the new script, no one mentioned Perry's problems. "This is a very professional group of people," says a show insider. "We read through the script, laughed and joked, just like any other week." While the other members of the celebrated sextet didn't let their concern show, one of the Friends retinue says, "[This] is the closest cast you can imagine. I can't believe that there hasn't been a great outpouring of love and support." As for those behind the camera, a crew members says that when he last encountered Perry, a week before he checked into rehab, he seemed "totally normal."

Of course, it is the particular talent of actors to put on a convincing show. The question now is whether Perry's ongoing problems will hurt his chances of getting new roles. "For the most part, I think that there's a genuine concern for him and a genuine concern that he get his life together," says Lisa Beach, a casting director. She speculates that, like Robert Downey Jr., Perry won't be hurt if he successfully seeks treatment. Another casting director concurs. "Alcohol and drugs," he says, "are diseases that people forgive." Certainly executives sounded forgiving last week. "Our thoughts are with Matthew," says Jeff Zucker, president of NBC Entertainment. "He has been a central part of the NBC family for so many years, and we fully support him taking these positive steps."

But there could be problems. Beach notes that all lead actors, regardless of their box office stature, are required to undergo physical examinations prior to production. "That's kind of a blanket thing for the underwriting or the bond company," she says, referring to businesses that help insure movie productions. While these exams do not typically include blook or urine analyses, one movie producer suggests that in a case such as Perry's, "a rider will be attached to the policy and he would probably have to take a drug test." If drugs were found, he adds, "he wouldn't get insurance and wouldn't be able to work in the film. He will be under much greater scrutiny."

In recent years Perry's health problems and addictions have attracted nearly as much attention as Jennifer Aniston's myriad hairstyles. In the mid-'90s he became dependent on the painkiller Vicodin, which he had begun taking for wisdom-teeth pain and injuries suffered in a Jet Ski accident. In 1997 the actor checked himself into Minnesota's Hazelden Foundation rehabilitation center, where he has said he kicked his pill addiction during a 28-day stay. "I don't think there's anything in the world that I can't face, having faced that," he told PEOPLE the follwing year. "That was the scariest thing that's ever happened to me. You get a whole new respect for yourself and life when you go through something difficult."

Over the next few years, as the 6-ft. actor's weight yo-yoed wildly, hitting a low of 145, Perry repeatedly felt compelled to shoot down rumors of an eating disorder. Last May, not long after Friends wrapped its sixth season, he checked into L.A.'s Cedars-Sinai Medical Center, complaining of stomach pains. As rumors circulated that he was suffering the side effects of an extreme high-protein diet, publicist Lisa Kasteler initially declared that Perry had "the flu." The actor then told PEOPLE that he was receiving treatment "for a serious stomach ailment."

Five months after his 2½-week stay at Cedars-Sinai, he owned up to the real problem: pancreatitis, a potentially chronic inflammatory condition that can be caused by either alcohol abuse or prescription drugs. "In my case, it was hard living and drinking hard and eating poorly," he told Us magazine. "You play, you pay." But he insisted there had been no prescription pills involved, maintaining, "I learned my lesson at Hazelden." As for alcohol, he said, "I'm also sober."

Throught the summer he stayed clear of the limelight, avoiding temptation. He visited often with his father, actor John Bennett Perry, near Santa Barbara, and stayed at the Laguna Beach home of his mother, Suzanne Morrison (once press secretary to Canadian Prime Minister Pierre Trudeau), and his stepfather, NBC correspondent Keith Morrison. Once the No. 2 ranked junior tennis player in Ottawa, Perry returned to the court and hired a personal trainer. He also reportedly steered clear of his old afterhours watering holes.

When he returned to the Friends set lasat August, Perry was 20 lbs. lighted, in stark contrast to the chunky Chandler who had closed out the previous season. "I was still healing," he would say of the weight loss. "I couldn't eat more than chicken soup." As Friends fans observed, he soon filled out again, and he emphatically denied tabloid stories that he was in need of a liver transplant. (On the day he left the hospital, he swerved to avoid an oncoming vehicle and crashed into a porch 200 yards from his former home in Hollywood Hills. Though his Porsche was totaled, he was uninjured, and police found no indication of drugs or alcohol.)

Since that time, apart from an accident last fall when the limo in which he was riding rear-ended another car, Perry's life had appeared to hum along tidily. After signing a $750,000-per-episode Friends contract last May, he moved into a four-bedroom house in Beverly Hills. At present, Perry, who has previously been linked with Julia Roberts and former ABC entertainment president Jamie Tarses, appears to have no love interest in his life, according to work associates.

His unforgiving schedule suggests that work remains his principle focus. As for his health, a source on the Sara set says Perry briefly checked into Dallas's Baylor Hospital in mid-January for what the production crew was told was "the flu." Baylor personnel decline either to confirm or deny the visit.

As always, friends and family are forming an impenetrable shield around the star to provide him with the space he needs to mend now. One pal says of Perry's current stint in rehab, "It's sad that he has to be [there]--and it's wonderful that he is." Then, he adds, "I think it's the greatest thing in the world that he's doing something about it."

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