With Monday's announcement by his publicist that "Friends" star Matthew Perry, 31, had checked himself into an undisclosed rehab clinic for an unidentified "addiction" for an unannounced period of time, Perry's "Friends" castmates, true to their all-for-one spirit, have offered no comment, PEOPLE reports in its new cover story. 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," a show insider tells the magazine. "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 was surprised by the cool reaction. That person told PEOPLE, "(This) is just 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 member says that when he last encountered Perry, a week before he checked into rehab, he seemed "totally normal."