Reds left-hander Dontrelle Willis left in the third inning against San Diego on Sunday because of a sore forearm.
Willis made his seventh start of the season and had trouble with his control. He gave up four runs on six hits and a pair of walks while retiring only eight batters. He also threw two wild pitches, one of them allowing a run to score.
After James Darnell's RBI single made it 4-0 in the third, manager Dusty Baker and a trainer visited the mound. Willis then walked to the dugout flexing and shaking his left hand. The Reds said he had a sore forearm and would be re-examined Monday.