He has gone from the X-factor to being as important to UCLA as milk is to a baby.
He is also an indicator of how fragile the Bruins have become--as fragile as Wayne Cook.
But that's not fragile at all, he argues.
It bothers him when others talk about his injuries: a knee ligament, torn in a high school all-star game, that kept him out of UCLA for a season; the same ligament, torn four years later, that cost him last season; a thigh muscle problem that cost him practice time in August and September; a bruised kidney that kept him out of the Arizona State game, lost last week, 9-3.
"I don't want people worrying about it," he said. "I don't want people saying, 'Well, he's injury prone.' This injury was a different type of injury than my knee. Most people who get hit like that, they're going to be hurting, too.
"If I barely get touched and my knee pops out, that's a different story. But the knee has healed up well. So, I don't want people to think, 'Well, Cook goes down again.' "
It has been a concern since before the Bruins began practicing in August. Cook, a junior, was considered the favorite in a three-quarterback race because of his experience in the program.
"But he has a knee," reminded Homer Smith, UCLA's offensive coordinator.
And when Cook was announced the winner of the quarterback derby, Ryan Fien and Rob Walker were reminded of his physical history and told to be ready.
Even when Cook showed that the knee could stand the pounding, Coach Terry Donahue spoke carefully about Cook's value to the offense, with frequent references to his inexperience and physical state.
An interception, thrown when UCLA was driving in the final moments of the season-opening loss to California, didn't help.
When the Bruins had turned their season around, Donahue was sold on Cook's value and grew, for him, effusive.
"The thing that's helped us as much as anything is the play we've gotten out of the quarterback," he said as the Bruins prepared to play Oregon State. "The fact that it has stabilized and that Wayne Cook has performed so well has really helped us."
A week later, Donahue said: "What's happened to our football team is that we've had good performances, namely from Wayne Cook. Often as your quarterback performs, your team performs."
Never was that--or Cook's value to the Bruins--better demonstrated than a week ago when the Walker-led offense sputtered and Arizona State ended the Bruins' seven-game winning streak, setting up a weekend kidney watch. Monday night, Cook passed a medical examination.
"No one wants to go into a game like this without all their guns loaded," Donahue said.
Cook's play has been steady, not spectacular. He ranks fifth among Pacific 10 quarterbacks, having completed 120 of 219 passes for 1,601 yards. He has thrown 16 touchdown passes--14 of those to J.J. Stokes--and only three interceptions.
In only three games, though, has he exceeded 200 yards passing.
His counterpart today, USC's Rob Johnson, has 255 completions for 2,978 yards and 24 touchdowns, with only four interceptions. And he averages 257.4 yards.
But UCLA's offense is more balanced than USC's, with stronger emphasis on the running game.
"If I only throw the ball 16 times Saturday, which I've done this year (against San Diego State), that means we're running the ball well and that's great," Cook said. "That means we're running the clock and their offense, which is very potent, doesn't have a chance to get on the field."
Today's quarterbacks are acquainted. When Johnson was in high school at El Toro, his brother, Bret, roomed with Cook at UCLA.
"I think he is a great quarterback," Cook said of Johnson. "He's obviously throwing with great accuracy this year, and he's scoring a lot of points.
"I pride myself on not throwing interceptions. I really concentrate on keeping the ball away from the defense. . . . Sometimes I'll miss wide-open receivers, but I've always been good at missing the defensive guys, too. It seems to me like Rob's the same way."
This season, the winner will go to the Rose Bowl.
"This is the kind of game you dream about," Cook said. "It's so important. . . . This game is going to have everything for me. It's going to have the pressure, so many people in the stands, the Rose Bowl. I'm just going to be interested in how I do."