Orioles righthander Jason Hammel was placed on the 15-day disabled list and will undergo arthroscopic surgery Monday on his right knee, the team announced Sunday. Hammel, who's been dealing with discomfort in the knee for several weeks, left Friday's start in the fourth inning with pain.

An MRI performed Saturday revealed that his ailment isn't serious, but an operation is still needed to remove a piece of cartilage, according to MLB.com. Hammel is disappointed with the injury but should be able to return in time to help during the team's September stretch run.

"I feel like I am letting the guys down if I miss starts," said Hammel. "I want to be part of this. It's tough, because my body is letting me down right now, and I feel so good. A lot of hard work to get where we are right now. It is what it is."

Hammel has been Baltimore's best starting pitcher this year, posting an 8-6 record with a 3.54 ERA, 1.24 WHIP and 106 strikeouts in 109.1 innings and 18 starts.