The Reds think the problem contributed to his wildness in his last few appearances. Chapman walked 12 batters and retired only four in his last four outings. Twice, he left the game without getting anyone out.
The worst appearance yet was Sunday, when manager Dusty Baker brought him in to pitch the ninth inning with a 9-2 lead against St. Louis. Chapman walked four of the five batters he faced, throwing 18 balls in 23 pitches. The Reds held on for a 9-7 win that kept them in first place in the NL Central.
"It was affecting his mechanics," Baker said. "You can see the last few outings, he hasn't been the same. He really hasn't complained, either."
The 23-year-old Cuban defector has struggled with his role in the bullpen this season. The Reds signed him to a six-year, $30.25 million contract last year, expecting him to be a starter. With the rotation full, they moved him into relief in the second half of the season, when he was pitching in the minors.
He was called up for the stretch drive and hit 105 mph on radar guns, helping the Reds win the NL Central. They decided to keep him in the bullpen for one more year and had him in the bullpen from Opening Day. He developed tenderness in his elbow last month, forcing him to rest for a few days.
Chapman said he started feeling some pain in the shoulder a couple weeks ago, but thought it was nothing out of the ordinary.
"I thought I was going to be able to get better in time," Chapman said through a translator. "At the beginning, it was just a small pain and I continued doing all my workouts. It was staying the same. Then, it started to increase a little bit."
Chapman said he had something similar one time when he pitched in Cuba. He said the shoulder problem interfered with his control. He hit 100 mph on the radar gun Sunday a couple times, but his velocity was down a bit overall.
The Reds have been trying to learn what his arm can handle when he's pitching in relief. He developed the tender elbow after throwing four times in five days, forcing the team to use him more sparingly. That time, he didn't tell Baker about the problem until it forced him out of a game.
Baker has been trying to get Chapman to be more open about injuries, something that was discouraged when he pitched in Cuba.
"He wasn't as reluctant this time as he was last time," Baker said. "He's learning more to be honest about things. It's a slow process. Where he came from, they don't say much about anything. It's a cultural thing as much as it's a physical thing."
The injury leaves Bill Bray as the lone left-hander in the bullpen. Chapman had been pitching in the seventh or eighth inning before he developed control problems. Bray will move into his role.
Smith was optioned to Louisville on May 5, when starter Homer Bailey came off the disabled list. Smith had a 5.29 ERA in 14 appearances with the Reds.