CHICAGO -- The Brewers announced Tuesday that David Riske was lost for the season to elbow surgery, but they were more hopeful than ever of bringing in a valuable replacement.

Prized right-hander Yovani Gallardo, out since he underwent knee surgery in early May, threw 50 pitches in a simulated game on Tuesday in Phoenix. He will throw again on Friday and could rejoin the Brewers next week, most likely as a reliever.

"There was always a chance that he would pitch before the end of the season," assistant general manager Gord Ash said. "But we weren't going to tell you guys that because we didn't want to be on the 'Gallardo watch.' ... The way that we approached it is that if he came back, it was a bonus to us. We didn't count on it. We didn't want to put undue pressure on him with a timetable."

Gallardo was mobile enough on Tuesday to cover first base, back up bases and do everything necessary to field his position, Ash said. Minor League pitching coordinator Jim Rooney and Steve Kline, the pitching coach for Milwaukee's rookie-level affiliate in the Arizona League, monitored Gallardo's outing.

Before Ash consulted with Rooney and Kline, there was some thought that Gallardo could immediately re-join the team, according to general manager Doug Melvin. Instead, he will pitch again on Friday in Phoenix.

"What we have to be careful of is that there is obviously a lot riding on these 12 games," Ash said, referring to Milwaukee's remaining regular-season slate. "We don't want to be foolish because there is a very, very bright future here. We're not going to take a short-term gain for a problem down the road."

Riske, meanwhile, has not pitched since Sept. 7, and revealed last week that he had a cortisone shot to relieve the pain from a bone spur in his right elbow that existed before the Brewers signed Riske to a three-year free agent contract in December.

A decision was made over the weekend for Riske to undergo surgery on Sept. 23 to shave down the spur.

"He was hopeful that with rest and rehab, it would come around, but he tried to throw on the weekend and it didn't react the way he had hoped," Ash said. "The only alternative now is to get that spur out of there."

Head team physician William Raasch will perform Riske's surgery. Even if the Brewers advance deep into the playoffs, Riske will not pitch until next season.

After posting a 2.46 ERA in 65 games last season with Kansas City, Riske was 1-2 this year with a 5.32 ERA in 45 games.

In other injury news, outfielder Gabe Kapler will join the Brewers on Thursday in Chicago to either continue his rehab from a shoulder injury or contribute as a pinch-hitter, Ash said. Kapler tore a muscle behind his right shoulder making a throw home last week and probably will not play the field again this season.