ALAMEDA, Calif. — The Oakland Raiders showed how potent their running game can be this season when they posted their first 300-yard performance in more than two decades in the second game of the season.

Repeating that this week could be tougher with the top two running backs Justin Fargas and Darren McFadden slowed by injuries.

The two missed practice today as preparations began for Sunday's game at Buffalo. McFadden watched practice with a protective boot on his right foot to protect his turf toe injury. Fargas also was on the sideline with a groin injury.

The injury to Fargas is more serious and the Raiders are not optimistic about his chances to play against the Bills.

"It doesn't look very good right now," coach Lane Kiffin said. "The sooner he can get back, the better for us. He's very valuable to us, especially in protections, so, hopefully, we'll have him back. But it doesn't look very good."

The Raiders play at home next week against San Diego and then have a bye, giving Fargas extra time to heal if necessary. Fargas, coming off his first 1,000-yard season, said he did not want to rush back and risk further injury.

Having quality backups in McFadden and Michael Bush makes that easier. McFadden is expected to return to practice on Thursday.

"I'm going to be smart with it. If I can go, I'm going to go, but we have guys back there that can get the job done and it's not like I feel the team can't do it without me or anything like that," Fargas said. "I don't feel pressure or anything like that. But our running backs can get the job done. That gives me more of a comfort level to know that I can rehab the best I can and get 100 percent healthy then come back and try to help the team."

Fargas got hurt running a pass pattern in the first half on Sunday at Kansas City. With Fargas out, McFadden got the bulk of the carries until he hurt his toe.

McFadden, the fourth overall pick in the draft, had an impressive second game in the NFL, rushing for 164 yards and his first career touchdown. It was the second-best performance by a Raiders rookie to the 221 yards Bo Jackson gained against Seattle in a Monday night game in 1987.

Bush finished the 23-8 victory for the Raiders, getting his first carries in a real game since breaking his leg in the opener of his final year at Louisville in September 2006. After missing almost two full seasons, Bush could be the featured back against the Bills depending on the health of McFadden and Fargas.

"I've been waiting to play for a long time so whatever they come up with I'm ready for it," Bush said.

He did well against the Chiefs, with 16 carries for 90 yards and a touchdown. He did have a fumble late in the game that could have been costly if the Raiders defense had not responded with an interception.

But Bush atoned for the mistake by clinching the game with his 32-yard TD run. Bush cradled the ball tightly on that carry and didn't give it up until he brought it to the sideline as a souvenir.

"That scared me so much," he said. "I just felt like had we lost that game, I would have felt like it was all on me. I had to come back with another statement and let everybody know, 'Sorry, I'm gonna keep this ball."'

Starting left tackle Kwame Harris also missed practice with a knee injury. Harris missed the game against the Chiefs with the injury and Mario Henderson made his debut. The Raiders mostly ran away from the inexperienced Henderson, who played well by not committing any false starts or allowing any sacks.

Receiver Javon Walker could not finish practice because of a hamstring injury.