In a classic good-news/bad-news scenario, Chicago Bears rookie tailback Cedric Benson suffered no serious structural damage to his right knee Sunday, but the team's first-round draft choice is expected to miss 3-6 weeks with a sprained medial collateral ligament. Benson was injured in the second quarter of Sunday's victory over San Francisco when his right knee buckled, then bent under him at a grotesque angle. Trainers immediately signaled for a cart to remove Benson from the field, he did not return, and he left Soldier Field on Sunday night with an immobilizer on his leg. "It looked a lot worse than it was," coach Lovie Smith said Monday. "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."