Mike O'Brien and his freshly injured right knee hadn't even been carried out of the stadium yet when team doctors began to prepare him for the worst: "You might never play football again," they told him on the bench during the fourth quarter of last December's BYU-Colorado State game.

"That's baloney," thought O'Brien, and indeed when BYU opened fall practice Thursday in Provo he was there, just eight months after going down with the knee injury.At best, O'Brien, one of BYU's best running backs and easily its best kick and punt returner, wasn't expected to be fully recovered for a year. But O'Brien, a fifth-year senior, didn't have a year; he had already used his redshirt year. "That's why I had to get back," he says.

O'Brien has come far fast. He was on crutches until March and couldn't start full-scale workouts until May. But a steady regimen of running stadium stairs, therapy, weights and stretching have put him back in uniform, albeit one with a knee brace. His knee is estimated to be about 95 percent of what it was before the injury, but one big test remains.

"It's all up here now," says O'Brien, pointing to his head. "Sometimes I'm a little hesitant."

There is still the problem of gaining confidence in the knee - the kind of confidence that will allow him to make sharp cuts and to run in traffic without hesitation.

"We'll bring him a long a little at a time and see how it goes," says BYU Coach LaVell Edwards.

Certainly, BYU can use O'Brien this season. At 6-1, 215 pounds, with thick shoulders and arms, O'Brien is the team's one big running back, and perhaps the best back to call on in those sticky short yardage situations that have cursed the Cougars recently. In a reserve role last year, O'Brien rushed for a modest 309 yards on 87 carries (a 3.6 per-carry average) but scored a team-leading seven touchdowns. He also caught 18 passes for 147 yards.

O'Brien's injury came out of nowhere - no one touched him. He was sprinting to the right, on a sweep, then planted to make a quick cut back to the inside and crumpled to the turf.

"I felt a burning sensation in my knee," he recalls. "Then it was like a window shade had snapped shut. I could feel it (the ligament) wrap up.

"The grass was real tight and trimmed short, like a golf green," he continues, trying to explain why the injury occurred.

O'Brien elected to have the injury treated by his family's doctor in Chicago. After undergoing surgery on Dec. 29, the long process of rehabilitation began. Ten weeks on crutches. Therapy. Learning to walk again. Running stadium stairs.

"I started feeling good after 10 weeks," says O'Brien, "and that was real encouraging. I already had full range of motion. I was able to run uphill, because that doesn't put much pressure on the knee. I got to know the stadium very well."

It wasn't until 3 1/2 months ago that O'Brien was able to do normal running, and by then he was ready to make up for lost time. "Not having a car helped," he says. "I ran everywhere." He also lifted weights, biked up Provo Canyon, stretched - a routine that required six to seven hours a day.

"Some people just have real good recuperative power," says Edwards. "Plus, the guy has just always been a hard worker."

"The thing that helped is that every day I felt better," says O'Brien. "Not being able to walk for three months was strong motivation." That, plus the possibility that he might never play again. But with eight tough months behind him, O'Brien most likely will be there when the Cougars open their season Sept. 1 against Wyoming.