Pittsburgh Steelers linebacker James Harrison underwent left knee surgery Wednesday, clouding his chances of returning in time for the start of the regular season.
Coach Mike Tomlin called the procedure "minor" but wouldn't put a timetable on when Harrison will be ready. The fourtime Pro Bowler and 2008 NFL Defensive Player of the Year will remain on the physically unable to perform list indefinitely.
The knee limited Harrison during organized team activities in May but Tomlin dismissed the idea that Harrison could have undergone the surgery during the spring and simply put it off.
"We address things as they arise," Tomlin said. "We felt like the procedure was necessary at this time, so we had it."
The 34-year-old Harrison has been one of the most dominant defensive players in the league over the last half-decade but has dealt with a series of setbacks during the last 18 months. He had surgery in February 2011 to deal with a bad back and missed a month last season when he fractured his right orbital bone in a loss to Houston.
Defensive end Brett Keisel, who sees Harrison regularly in the team's weight room, doesn't think Harrison will be out for an extended period.
"They said he should be fine," he said.
With Harrison and fellow outside linebacker Jason Worilds out, it means second-year linebacker Chris Carter will see plenty of action Sunday when the Steelers face the Indianapolis Colts.
