MILWAUKEE -- Right-hander Yovani Gallardo underwent successful surgery Tuesday to repair a torn ligament in his right knee, but the Brewers are still working under the assumption that Gallardo will not pitch again this season.

Gallardo tore the anterior cruciate ligament in his knee when he tangled with Cubs outfielder Reed Johnson near first base at Wrigley Field on May 1. Gallardo remained in the game and recorded another five outs, but the extent of his injury was revealed the following morning.

Dr. William Raasch, the Brewers' head physician, performed the surgery early Tuesday morning. The repair took less than an hour.

"[Raasch] said it was very, very straightforward," Brewers assistant general manager Gord Ash said. "It went very well."

It was Gallardo's second surgery this year. He tore ligament in the other knee just before the start of Spring Training and underwent an arthroscopic procedure that sidelined him about a month before he began throwing. Gallardo spent the first three weeks of the regular season on the disabled list.

Ash would not offer a timetable for Gallardo's return from the second surgery.

"He rehabbed well from the first one," Ash said. "This one is more extensive, obviously. We'll see how it goes. ... What will dictate how quickly he comes back is how he re-learns to use the knee."

Gallardo will begin his rehab on Wednesday and will remain in Milwaukee until he progresses to the point of baseball activities.