Pernell McPhee underwent arthroscopic surgery on his right knee Friday morning and is out indefinitely, coach John Fox said.

The Bears put McPhee on the active/physically unable to perform list Wednesday when an “irregularity,” as Fox described it, was discovered in his knee. Friday’s procedure casts doubt on McPhee’s availability to participate in any preseason practices or games and even the regular season.

“The extent of the scope is just a cleanup,” Fox said. “We’ll keep you posted as far as the timeline. I’m not going to try and predict that.”

McPhee’s scope is the third such procedure he is known to have had on his right knee. He had two in 2012 as a member of the Ravens and played effectively in subsequent seasons.

This procedure is on a different knee than the one that required surgery and landed McPhee on the PUP list in 2016. Last season, McPhee missed the first six games while recovering and played only 25.5 percent of the Bears’ defensive snaps during the regular season.

His absence leaves the Bears without one of their most rugged edge defenders against the run.

rcampbell@chicagotribune.com

Twitter @Rich_Campbell