(CBS) Bears linebacker Pernell McPhee’s unexpected placement on the physically-unable-to-perform list to open training camp stems from an issue in his “other knee,” general manager Ryan Pace said in an interview with Dan Bernstein and Jason Goff on 670 The Score on Thursday afternoon.

Pace didn’t specify which knee is currently an issue for McPhee and the team didn’t clarify in it’s news release, but it’s worth noting that he had left knee surgery early in 2016. That procedure and rehabilitation slowed McPhee a great deal in 2016, as he missed the first six regular-season games on the PUP list.

McPhee’s current status on the PUP list can be changed at any time in the preseason. He can’t practice with the team until he’s removed from the PUP list, though he can partake in team meetings and receive the usual medical treatment.

The Bears didn’t forsee McPhee’s newest knee problem coming. He had offseason shoulder surgery and no knee procedures recently.

“We did our physicals yesterday, we had the conditioning tests yesterday,” Pace said. “You know, it’s inevitable. It’s part of the game. These guys come in, do their physicals and sometimes there’s things that surprise you. And being honest with you, Pernell’s had a good summer, a good offseason. His weight is at a good spot right now, and he came in and his knee was a little aggravated in the physicals that we had yesterday. And honestly, it’s the other knee. So we’re kind of working through that right now, trying to get that to calm down right now. And you know, PUP is a tool the NFL gives us. We should use it to our advantage, and I feel like we’re doing that, just being thorough. What exactly do we have here and what’s the best course of action?”

McPhee’s continued knee problems are a great source of concern for the Bears. Knee injuries have now slowed him in each of his three seasons in Chicago after the team gave him a five-year deal worth just shy of $16 million guaranteed and up to about $39 million.

McPhee had 16 tackles and four sacks in nine games last season.

Listen to Pace’s full interview below.

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