He will become the Brewers' second fill-in starter in three days. The team also promoted Mike Burns from Nashville this week to start Thursday in place of the injured Dave Bush.
"I've increased my running and my conditioning just in case," McClung said after getting the news on Wednesday. "I'm glad to have the opportunity, but then again, I wish Bush wasn't hurt and I wish Manny wasn't struggling. You never want those things to happen."
Macha told McClung in Spring Training that he was considered the Brewers' sixth starter, the first line of defense should anything happen to the starting five. But Macha was hesitant to live up to that promise this week, even when it became clear that the Brewers would need reinforcements, because McClung has been so valuable in the bullpen.
In 28 relief appearances, McClung has a 3.24 ERA. He's held opponents to a .242 batting average.
"We talked about a bunch of different scenarios," Macha said. "I hate taking him out of the bullpen because he's been so valuable to us out there. It's kind of a double-edged sword for him because he's pitched so well for us out of the bullpen ... but I think he's relishing the fact that he's going to start. By keeping him [in the bullpen], it would be like punishment for him."
McClung pitched one inning out of the bullpen on Tuesday as a tune-up for his start. He has not thrown more than 48 pitches in any of his appearances this season, but Macha figures he might be able to get 70-75 pitches out of McClung on Saturday.
Last year, McClung made a similar move. He threw 68 pitches in five innings in his first start at Washington on May 24, then threw 85 pitches five days later against the Braves.
"I'm a big old tough guy; I'm going to be all right," McClung said. "Last year, I wasn't stretched out either."
With McClung in the rotation, left-hander Chris Narveson is the Brewers' long reliever. He will likely be on high alert on Saturday.
"We'll see how that goes," Macha said. "If you bring someone out of the bullpen to start if it's a doubleheader, you're probably kind of hoping to get five innings out of him. It will depend on how he's going. I've described him as a 'horse.' He has good stamina."
McClung is in line for three starts, including his outing on Saturday, before the All-Star break.
With McClung in the fold, all five Brewers starters are right-handed. For that reason, Macha said the Brewers considered recalling Parra after the left-hander pitched seven strong innings in a tough loss for Nashville on Tuesday night.
"It is what it is right now. Those are our starters at this moment," Macha said. "The start by Manny was encouraging. Is he ready to come up here right now? I'm not so sure, and I think that's [Triple-A pitching coach Chris] Bosio's opinion, also."
McClung had to ask reporters who he would be facing this weekend. They informed him the Giants would be in town.
"I'm honored that I've been given this opportunity and I'll try to make the most of it," he said.