CHICAGO – Ryan Dempster, one of the few bright spots in a dismal season for the Cubs, landed on the 15-day disabled list Monday because of tightness in his latissimus dorsi muscle.

Dempster is expected to miss at least his next two starts.

The tightness first occurred during Dempster’s June 5 start at Milwaukee. Since then, it has been increasingly difficult for Dempster to keep the muscle loose.

The tightness, however, didn’t adversely affect Dempster’s past three starts, in which he strung together 22 consecutive scoreless innings.

“Any time you have a muscle tighten up on you, it’s something you don’t want, especially as a pitcher,” said Dempster, who owns a 3-3 record and ranks third in the majors with a 2.11 ERA this season. “With your lat like that, to get on the mound, I was a little shocked. It didn’t feel very good, but I was able to get the outs. Just try to get it better right now.”

Manager Dale Svuem said there is no timetable for Dempster’s return.

Soto activated: Sitting on the sidelines as the Cubs struggled wasn’t easy for catcher Geovany Soto.

An eager Soto returned to the lineup Monday against the Sox after he was activated from the DL. Soto had arthroscopic surgery on his a left knee May 18 and rejoined the team after a five-game rehab stint with Triple-A Iowa.

Preparing for Rizzo: As top prospect Anthony Rizzo crushes opposing pitching in Iowa, the Cubs already are making adjustments for his big league arrival.

Sveum started Bryan LaHair in right field for the first time this season and gave Steve Clevenger his first start at first base. With Alfonso Soriano filling the designated hitter spot, the Cubs got a glimpse of what the lineup – specifically the outfield – could look like when Rizzo is called up.

“We all know there’s a day when Rizzo is going to be here, so it’s kind of getting him acclimated to the outfield, too,” Sveum said.

Sveum called LaHair on Monday morning to notify him of the change. LaHair occasionally shags balls but hasn’t played in the outfield since last year. In 14 starts in the outfield, he committed one error.

“I think in the back of my mind there was always the thought of me moving to the outfield at some point,” LaHair said. “It’s not like it’s a complete surprise. … It’s a good new challenge. I’ll be working defensively in a different spot.”