Dempster was put on the 15-day DL with back muscle tightness.
The 35-year-old hurler has an ERA of 2.11 after winning his last three starts. He has not allowed a run in his last 22 innings.
Dempster is also the subject of trade rumors as the last-place Cubs look to stock up on prospects.
To take his place on the roster, Chicago activated catcher Geovany Soto, who hasn't played since May 16 due to a torn meniscus in his left knee.
The Cubs also optioned catcher Wellington Castillo to Class AAA Iowa and recalled pitcher Scott Maine from the farm club.
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