LAKE FOREST, Ill. (Nov. 14, 2005) -- Cedric Benson 's first NFL start could be his last one of the season.

The Chicago Bears' top draft pick sprained the medial collateral ligament in his right knee during the second quarter of the team's game against the 49ers. He will be out an undetermined time, perhaps a month.

Coach Lovie Smith said he expects Benson to play again this season.

"It looked a lot worse than it was," Smith said. "I'll say that. ... We think right now it's week to week. Hopefully we'll get him back before long. We don't know exactly how long it will be, but we know that we'll get him back some time this year."

Benson got the start against San Francisco with leading rusher Thomas Jones sidelined by sore ribs, and gained 50 yards on 12 carries. As he was being hit for a 2-yard loss by San Francisco's Isaac Sopoaga in the second quarter, Benson's right leg twisted under him and he had to be wheeled off the field on a cart.

Adrian Peterson took over and finished with 120 yards on 24 carries and had a TD run in Chicago's 17-9 victory.

"Cedric Benson was having a real good game yesterday before he went down with the injury. Each time he plays we get a chance to see more and more what he'll be some day for us," Smith said. "And Adrian Peterson just continues to play well every time we give him an opportunity."

Benson, the sixth-leading rusher in NCAA history before he left Texas with 5,540 yards, was the No. 4 pick overall, but held out of training camp and didn't play in the preseason.

Just as he was starting to feel comfortable, he's got another setback. Benson was not available for comment.

"When Cedric can come back and help us win and play injury-free, we'll get him out there, too," Smith said. The Bears (6-3), leading the NFC North with a five-game winning streak, have seven games remaining.

"We definitely think he (Benson) can be part of the stretch run," Smith said. "That's why when you see an injury like that, you are expecting the worst and you find out it's not that bad.

"We need all of our guys and Cedric is a part of what we are trying to do running the football. Other guys have to pick up the slack until he gets back."

Smith also said the Hall of Fame called asking for Nathan Vasher 's jersey and the football from his 108-yard return of a missed field goal -- the longest play in NFL history.

"He's going to get quite a bit from it," Smith said of Vasher. "It was a great run, aided by a lot of great blocks."