Guzman had a 3-1 lead in the fifth against the San Francisco Giants, and was one out shy of qualifying for the win when he was pulled. The right-hander had fallen behind Steve Finley, 3-0, in the count with two out and one on. Cubs manager Dusty Baker, pitching coach Larry Rothschild and assistant trainer Ed Halbur went to the mound after Guzman was seen flexing his right arm.
The pitcher threw a couple warmup pitches, and stayed. Guzman then walked Finley, threw one pitch to Omar Vizquel, a ball, and head trainer Mark O'Neal went to the mound with Baker. Guzman was then pulled.
"He's OK," Cubs manager Dusty Baker said. "His forearm cramped and he couldn't get the cramps out of there. He was throwing the ball good. He needed one more out to try to get his first victory. He couldn't go any longer. It's nothing structural. It's something he'd been fighting in the Minor Leagues. We just have to find out why he cramps. He'll be fine."
Guzman's next start would be Friday in Atlanta.
"I had this problem twice in Triple-A," the rookie said. "I've been drinking water and Gatorade and that kind of stuff. [Team orthopedist] Dr. [Stephen] Gryzlo said it's normal. The intensity I was using in the game -- cramps happen."
Before the game, the Cubs placed catcher Michael Barrett on the 15-day disabled list, the 19th time they've used the DL, which is a team record. Outfielder Jacque Jones had to leave Sunday's game after eight innings because of an infected left tear duct. His status was day-to-day.
Guzman, 24, missed much of last season because of a strained right forearm. He has yet to win in seven big-league starts.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.