Jonathan Vilma having knee surgery

New Orleans Saints linebacker Jonathan Vilma is undergoing knee surgery Thursday in Philadelphia that is expected to sideline him for the remainder of the preseason with the hope he will be back to start the regular season, according to a source familiar with the procedure.

The surgery is being performed to reduce some of the swelling and discomfort Vilma has been experiencing in the knee.

If his recovery goes well, the Saints are expecting he should be ready for their Sept. 8 regular-season opener against the Atlanta Falcons.

Saints coach Sean Payton said Thursday night it remains unclear how long Vilma will be sidelined.

"We'll have him back and we'll kind of go from there," Payton said.

Vilma, 31, has missed six of the past eight practice sessions and did not participate in the first preseason game.

The team has not revealed what Vilma's injury is, and Payton said Wednesday he wasn't going to discuss the situations of any injured players.

The 31-year-old Vilma has had numerous surgeries on his left knee during the past two seasons. He missed five games in 2011 and started last season on the physically unable to perform list. However, Payton stopped short of saying he viewed Vilma's latest surgery as a setback.

"This is a little different procedure, so we'll how he does when he gets back," the coach said.

Information from ESPN.com's Pat Yasinskas and The Associated Press was used in this report.