Boston Red Sox left-hander Rich Hill was placed on the 15-day injured list on Saturday, one day after leaving his start against the Chicago Cubs with a sprained left knee.

Right-handed pitcher Phillips Valdez was called up from Triple-A Worcester to fill Hill's spot.

Hill had a 4-0 lead through four innings Friday before exiting during a three-run fifth inning. He said he felt a "pop" in the knee on a breaking ball in the fifth and in the moment thought it was something he could pitch through.

Hill appeared to be shaking his left leg at one point in the fifth and was visited by an athletic trainer. He exited after hitting a batter to load the bases with two outs. The Cubs would go on to rally for a 6-5 win.

"I feel stupid for staying in, to be honest with you, stubborn," said Hill afterward, adding that he "felt great" before the fifth inning. "Put us in a really bad position, and unfortunately, that falls on me, my stubbornness staying in and wanting to compete."

Hill, 42, is 4-4 with a 4.20 ERA this season.