The Boston Red Sox have placed Clay Buchholz on the disabled list with a hyperextended left knee.

Buchholz has been struggling this season and the Red Sox say the right-hander suffered the injury during Monday's start against the Atlanta Braves.

The decision to place Buchholz on the DL came after a bullpen session on Wednesday.

"When he got into the bullpen, probably the 18- or 20-pitch mark, there was some feeling of some instability," John Farrell said. "Can't say that it's structural, but when he tried to get increased intensity and get some finish to pitches, there was that sensation that was being felt, and we shut him down at that time. As I mentioned before he went out to the bullpen, we weren't going to put him at risk if he felt anything coming out of that situation the other day. That's where he felt it; it was just with that instability trying to get through some pitches."