ENGLEWOOD, Colo. — Denver Broncos wide receiver Javon Walker could miss six weeks after undergoing surgery on his right knee, although coach Mike Shanahan said Friday he's hopeful it will be less.

"I heard the doctor estimate it at six weeks. We'll get a better feel on it next week or so," Shanahan said.

Walker, who missed the Broncos' last two games because of excessive swelling and pain, tore his ACL during the 2005 season-opener with the Green Bay Packers. He had two surgeries to repair the knee that season and needed a follow-up operation around the time he joined the Broncos in a draft-day trade in 2006.

The Broncos could certainly use his big-play ability. They are 2-1 when he plays and 0-2 without him. Walker had 17 catches for 220 yards in the team's first two games before being held to just two catches and 10 yards against Jacksonville in Week 3.

The Broncos also might be without shutdown cornerback Champ Bailey when they host Pittsburgh on Sunday night. Bailey returned to limited practice Friday after missing the rest of the week because of a strained right quadriceps.

"If I feel like if I can go 100 percent, I'm definitely going to go out there," Bailey said. "I feel like I've got 2 1/2 days to get myself ready. That's enough time. I'll go out there and see how it feels."

Bailey has missed only two games in his NFL career.

"He'll know if he can play or can't play," Shanahan said. "Champ is pretty direct. He's a very tough player. Obviously he'd like to help our football team win, but he knows if he's injured or not."

The struggling Broncos can't afford any more injuries.

Tight end Nate Jackson is lost for the year with a groin injury. The team also placed tight end Stephen Alexander on injured reserve Thursday because of a calf injury.

Center Tom Nalen is out for the season with a torn biceps. Chris Myers has shifted from guard to center, and Chris Kuper has taken over Myers' spot on the offensive line.

Tight end Tony Scheffler's return to form last week should provide a boost to quarterback Jay Cutler and a struggling red zone offense. Scheffler became one of Cutler's favorite targets near the goal line last season.

"I think we kind of tried to push him out there a little bit too early," Cutler said. "He felt like he should be making plays for us like he did at the end of last year. Hopefully we can use him a little bit this week, use some two tight end sets and have him stretch the field."

RAIDER INJURIES: Oakland Raiders defensive tackle Gerard Warren and linebacker Sam Williams will miss Sunday's game against the Kansas City Chiefs with injuries.

Warren Sapp, the team's other starting defensive tackle, was listed as probable with an ankle injury. He had missed practice the previous two days.

YOUNG TO BE GAME-TIME DECISION: Titans quarterback Vince Young will be a game-time decision Sunday against Houston after he took one series of snaps with the scout team Friday.

TANK BACK ON PRACTICE FIELD: Suspended defensive tackle Tank Johnson practiced with the Dallas Cowboys for the first time Friday, disappointed that commissioner Roger Goodell didn't shorten his eight-game ban but glad to be back on the field.

Johnson was signed by Dallas after getting cut by the Chicago Bears and can't play in a game until Nov. 11 against the New York Giants. He said he'd hoped Goodell would agree to shorten his suspension for violating probation on a gun charge to six games but will settle for the three weeks of practice he was granted.

RAVENS' LEWIS QUESTIONABLE: Baltimore Ravens middle linebacker Ray Lewis has an injured knee and is one of several key players who could miss Sunday's game against Buffalo.

Lewis will be a game-time decision, coach Brian Billick said Friday.