Per Steve Melewski via MASN:
Orioles pitcher Jason Hammel told reporters a few minutes ago that he has decided he will have surgery on his right knee. The arthroscopic procedure will take place at Johns Hopkins Hospital in Baltimore on Monday.
"Obviously, it's not what I want to do, but it's what needs to be done," Hammel said. "I can't keep pitching on a bad leg and start doing things with my arm and hurting stuff there. I'm bummed out, but it will be a pretty routine surgery. I figure a few weeks, maybe four weeks hopefully for the return, which gets me back in time to help the club.
"They'll go in and pull out the cartilage that is floating around and see if there is anything else in there that we haven't caught. They told me three to four (weeks to be back) right now. It could be later than that, it could be earlier than that if I'm a superhero.
"It's a decision that had to be made. I want to help the club, but it's another opportunity for someone else to come help out and I'll get back to doing my thing when I get healthy."
Hammel is 8-6 with a 3.54 ERA over 18 starts and 109 1/3 innings. He left Friday's start after throwing a 1-2 pitch to Brennan Boesch in the top of the fourth inning. Hammel said he could have put off surgery and tried to rest and rehab the injury.