Zambrano suffering from tightness in right arm

The Chicago Cubs might lose another arm from their rotation.

An MRI on Monday confirmed that Carlos Zambrano is suffering from tennis elbow.

The right-hander, who lasted just 3 1/3 innings against the Nationals on Saturday, is in jeopardy of missing his next start with tightness in his right arm above and below the elbow, Cubs athletic trainer Mark O'Neal told MLB.com on Monday.

Zambrano, who is scheduled to start Friday against the White
Sox, will throw on the side Wednesday in Pittsburgh. It was not
clear who would start if he is not available.

"Carlos is pretty anxious to get right after it," O'Neal told MLB.com. "The plan now is try to do a side session on Wednesday and go from there."

Zambrano said Sunday that he felt as though he had "concrete in my arm" after his outing against Washington. However, he sounded confident he'd make his next start if at all possible.

"I'm a horse," he said Sunday. "They'd have to kill me [to get him to miss a start]."

Zambrano is 3-2 with a 4.09 ERA in eight starts. He threw 136 pitches in his previous outing, a complete-game victory over Philadelphia on May 8.

Information from The Associated Press was used in this report.