Denver ? The Denver Broncos have avoided the big injury this season. Finally, luck caught up with them, when starting cornerback Darrent Williams pulled up hurt.

Williams, the rookie who was elevated to a starting position in Week 3, is expected to miss four weeks – maybe less if rehab goes good – after hurting his right groin while chasing down Baltimore’s B.J. Sams on the opening kickoff Sunday. Williams made the tackle after an 87-yard return, but played only a few plays after that.

The second-round draft pick from Oklahoma State was being evaluated by an outside doctor Tuesday and was not at Broncos headquarters. If coach Mike Shanahan’s four-week estimate is correct, it would mean Williams wouldn’t be back until the second week of the playoffs, which would be Denver’s first game if it holds onto the second seed in the AFC.

Shanahan declined to give specifics on the injury, saying only that Williams had “pulled” his groin.

The Broncos (10-3) lost Champ Bailey for two games earlier in the season with a hamstring injury, but otherwise have gone through the year relatively free of injuries.

This, however, marks the third straight season Denver has lost a key member of the defensive backfield in December. The last two years, those seasons have ended with ugly losses inflicted by Peyton Manning and the Colts in the playoffs.

“It’s a high-risk position,” defensive coordinator Larry Coyer said. “It’s the nature of their body style. Those guys get injured at a high rate. We have been very unfortunate.”

Williams has two interceptions this season, including one he returned 80 yards for a touchdown at Oakland last month. He has 49 tackles and one sack.

His injury likely opens the door for another rookie, Domonique Foxworth, to start opposite Bailey. It was the strong play of Williams and Foxworth that compelled the Broncos to part ways with Lenny Walls last month.