Dempster has been pitching through the soreness, with 22 consecutive scoreless innings over his last three starts, all wins. His 2.11 ERA ranks second in the National League.
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It's Dempster's second DL stint of the season. He missed two starts in April with a quadriceps injury.
The Cubs are calling it a precautionary move and said the injury is not serious.
"We want to nip this in the bud and make sure it doesn't turn into a strain or anything like that," President Theo Epstein said. "It's unfortunate because he was throwing as well as anyone in the game. But he knows his body really well."
Dempster is expected to be traded before the July 31 deadline. This at least will delay the inevitable.
"Oh, then I should've pitched through it," Dempster cracked. "I'm not really worried about that. I'm more worried about trying to get healthy."
Epstein wouldn't talk about trade rumors involving Dempster but said, "Generally when players have these sort of minor injuries, it's typical to wait until they come back and re-establish health before engaging in any serious trade talks."
Dempster said he felt the latissimus dorsi muscle pull in a June 5 start against the Brewers, and "it got harder and harder to get loose and maintain."
The Cubs called up Scott Maine from Triple-A Iowa to take Dempster's roster spot, while Randy Wells will take his spot in the rotation, starting Wednesday against the White Sox.
Epstein on fans: Tigers fans took over Wrigley Field last week, which upset some players.
"Our fans are great and really supportive," Epstein said. "But if we want to have a sort of dominating home-field advantage, then we need to play well and earn it. It's on us."
Cubs fans also booed Alfonso Soriano on Saturday for failing to run on a hard-hit line drive that was dropped. Epstein called it an "unfortunate natural reaction" by Soriano, adding that if fans were grading Soriano's hustle throughout the year, "he would get very high marks."
"I like that our fans hold our players accountable to play hard and play the game the right way," he said. "But I also think it's going to be hard to be on the right side of the line every time."
Soto returns: Catcher Geovany Soto returned from the disabled list and was in the starting lineup, with backup Steve Clevenger at first base. Welington Castillo was optioned to Iowa.
"It's important for Welington's development that he continue to play," Epstein said.