SAN FRANCISCO -- Brewers starter Claudio Vargas will be in Milwaukee on Monday for an examination of his sore back, and the right-hander told a radio reporter Sunday that he expected to go on the disabled list.

Vargas lasted only two-thirds of an inning Friday against the Giants and left the game complaining of "a bad back," assistant general manager Gord Ash said. Dr. Michael Young, a member of the Brewers' medical team, was in San Francisco and detected muscle weakness.

Once he returns to Milwaukee, Vargas will be examined by head team physician William Raasch.

"I don't know about the disabled list, but he's going to Milwaukee to see Dr. Raasch [Monday] and we will go from there," Ash said.

Milwaukee's starting pitching was already jumbled heading into a key series between the first-place Cubs and the second-place Brewers at Wrigley Field. Jeff Suppan will start the opener Tuesday, but manager Ned Yost had yet to announce plans for Wednesday or Thursday because he was waiting for word on disabled right-hander Ben Sheets (blister). Vargas' regular day to pitch would have come Wednesday.

Despite Friday's ugly loss to the Giants, in which the Brewers rallied to spare Vargas the loss, the team is 16-7 in his starts. He is 10-4 with a 5.13 ERA in 25 games, including 23 starts.

Even if Sheets returns during the Cubs series, the Brewers would need another starter by the end of the week because left-hander Chris Capauno was moved to the bullpen. Options include moving Capuano back to the starting rotation, giving lefty Manny Parra a spot start or recalling right-hander Carlos Villanueva from Triple-A Nashville, where he was sent last week to make two starts to prepare for September with the Brewers.

Villanueva had been struggling in relief with the Brewers, but he pitched four scoreless innings in his first start at Nashville.