NAPA, Calif. — The Oakland Raiders have finally discovered something rookie Darren McFadden can't do.

He can't say no.

Run the ball? Of course. Flatten someone with a block? Not a problem. Run a pass route as crisply as any receiver on the roster? Sure thing. Line up at quarterback? You got it.

At training camp, McFadden, the fourth overall pick of the NFL draft, has been a rumbling renaissance man, the most complete Raiders rookie at this stage since Marcus Allen — only faster. (The freakishly fast Bo Jackson is not part of that argument because he joined the team midway through the 1987 season.)

Coach Lane Kiffin said McFadden is "shockingly good" at taking instructions once and seamlessly incorporating them into his game.

"We've all had great players at times, but they take a long time," Kiffin said. " `Hey, we're going to run this route that we've never run before.' Well, it takes a whole week to get them used to the steps and different coverages and stuff.

"Then there are people that you tell it to them one time and then all of a sudden they look like they've been doing it forever. He seems to be one of those guys so far."

Even McFadden's main competition for carries is intrigued by what he has seen.

"Any time you get an athlete like that, a playmaker guy, you want to see what he can do," said running back Justin Fargas, who is coming off his first 1,000-yard season. "You're excited to have him, and you want to get him in position to get his hands on the ball. ... I think he can handle it."

Of course, it's only training camp — the Raiders play their second exhibition game Friday night at Tennessee — and McFadden has faced mostly generic defenses. The pace picks up significantly when the games really count. But he's showing fluid moves and bursts of speed in practice that are raising eyebrows. He has uncommon speed for a back his size — he's listed at 6 feet 2, 210 pounds but looks wider — and some scouts have compared him to a young Marshall Faulk.

Kiffin's concern is this: He and his coaches need to be careful not to pile too many responsibilities on McFadden, tempting as that might be. That happened to Reggie Bush early in his career at USC, when Kiffin was an assistant there.

"We screwed Reggie up at first," he said. "We had him doing too much and he wasn't as good a runner as he could be. We had him out wide running routes, running double moves, all that kind of stuff. Then all of a sudden we were saying, `Man, this guy's not running the ball that well.' And if you look at that freshman year, he wasn't lighting it up on the ground.

"He had some good things where he was catching the ball and everything else. But we were doing all this stuff, and we weren't really getting his best."

By Kiffin's thinking, the same thing has slowed Bush's development in New Orleans. He has shown flashes of excellence there, but also has disappeared for long stretches.

Kiffin said Saints Coach Sean Payton "did so many things with him. That first year he caught 80 balls and he was lining up all over the place. All of a sudden he's getting like 3.2 yards a carry."

So the trick with McFadden will be finding a balance, maybe lining him up at receiver now and then but not dropping a double-thick playbook on him.

"The one thing you don't want to do is do so many things that he does nothing well," the coach said. "He's got to be really good at things before you do too much. We put a lot on him, but if all of a sudden you go back and after, say, Week 2 or Week 3 of preseason, you evaluate and say, `Geez, this guy's not even running inside zone well. Well what are we doing throwing all these passes and screens and all this different stuff with him?'

"It's really up to him more than it's up to us. How far can he take it? How many things can he master and do really well?"

Until this week, Kiffin had to grope to find any flaw in McFadden's performance at camp. But the rookie fumbled twice in Monday's practices — a flashback to some football-protection problems he had at Arkansas last season — and Tuesday didn't seem to be at his best.

"You have your up days and you have your down days," said McFadden, who ran for 48 yards in 12 carries in the Raiders' 18-6 victory over San Francisco in an exhibition opener last week. "I guess those just weren't my days."

For those keeping count, McFadden's ups vastly outnumber his downs. And it's not as if the Raiders had a shabby running game to begin with; they were ranked sixth in 2007, have a solid back in Fargas and a promising prospect in Michael Bush.

It looks like the real challenge for the Raiders will be getting their passing game on track so defenders can't load up against the run. Quarterback JaMarcus Russell made a few what-were-you-thinking and where-were-you-looking passes at camp Tuesday.

At the same practice, the Raiders lined up McFadden at quarterback in what they call the "stag" formation.

"It's a joy to me because I played quarterback all the way up to my sophomore year of high school," McFadden said. "So it brings back memories for me."

Maybe the quarterback thing is just a summer gimmick, but it could be something more. With the way McFadden has performed so far, it doesn't hurt to take a peek.