MILWAUKEE -- The Brewers' slumping starting rotation endured another loss on Tuesday, when the team placed right-hander Claudio Vargas on the 15-day disabled list with a lower back injury.

Milwaukee did not announce a corresponding roster move, leaving open the possibility that All-Star starter Ben Sheets could return to the rotation this week during a key National League Central Division showdown with the Cubs.

Manager Ned Yost said over the weekend that he hoped to use Sheets, who has been receiving treatment for a blister on his right middle finger, on Wednesday or Thursday against the first-place Cubs.

To guard against unforeseen circumstances, the team typically does not activate players, especially pitchers, until the last moment before they play.

Both Sheets and Vargas are 10-4 this season, though Sheets leads in the ERA category, 3.39 to 5.13.

Vargas' move to the DL was retroactive to Aug. 25, a day after he lasted only two-thirds of an inning in a loss in San Francisco. Vargas told a Spanish-language reporter over the weekend that he had been managing a sore back for some time, and Vargas traveled after the series back to Milwaukee to see head team physician Dr. William Raasch.

Right-hander Jeff Suppan was scheduled to start Tuesday's series opener against the Cubs. The Brewers sit 1 1/2 games back in the NL Central.