ATLANTA -- Rod Coleman underwent surgery Monday to repair a ruptured right quadriceps that could keep the Atlanta Falcons' standout defensive tackle sidelined into September.

Falcons spokesman Reggie Roberts confirmed that Coleman was injured in a recent boating accident.

Losing Coleman, a Pro Bowl selection in 2005, is a big blow to a defense that will open its first training camp under new coach Bobby Petrino with as many as six unproven starters.

Atlanta general manager Rich McKay said Sunday that weakside linebacker Demorrio Williams had surgery last week after tearing a pectoral muscle in the team's weight room.

Williams might not return until the first month of the regular season. Petrino and McKay indicated that rookie Stephen Nicholas, a fourth-round draft pick from South Florida, will open mini-camp May 11 as the weakside starter.

Coleman's injury means that Jonathan Babineaux likely will take over at tackle next to right end John Abraham.