The Cubs trailed, 6-0, when Parker entered in the eighth inning with the bases loaded and one out against the White Sox. He struck out pinch-hitter Brent Lillibridge and fell behind 3-0 to Alejandro De Aza. On his last pitch, he came off the mound awkwardly and athletic trainer Mark O'Neal immediately went to the mound.
"On the 1-0 pitch, I felt a cramp a little bit," Parker said. "On the 2-0 pitch, I tried to throw it and it tightened up. On the second pitch, when I pushed off the rubber, that's when I felt it and I threw the pitch with my upper body. I didn't have a choice."
Parker tried to talk O'Neal and manager Dale Sveum into letting him throw a couple pitches to test his leg, but he was lifted from the game.
"It feels fine right now," Parker said. "As far as pushing off the mound, we'll see. I feel fine now, I feel like I could run. We'll take it day by day and hopefully I wake up and I'm 100 percent."
This was Parker's second Major League appearance. The right-hander was called up Thursday from Triple-A Iowa where he was 5-for-5 in save opportunities.