Cashner has primarily served as San Diego's eighth-inning specialist this season and is 3-3 with a 3.81 ERA in 27 appearances. The move to the rotation comes after an injury to Eric Stults, who hit the 15-day disabled list with a left lat injury.
However, manager Bud Black said this won't just be a spot start for Cashner.
"We'll see how it goes. Ideally, he'll pitch into the third inning and we'll see where his pitch count is," Black said. "It's good for him. His mix of pitches will enable him to start moving forward if we think that's the way to go."
If all goes well, Cashner will then be sent straight to the Minors to begin conditioning his arm.
The right-hander spent most of his Minor League career as a starting pitcher. With the Cubs farm system, he went 10-8 with a 2.82 ERA in 48 appearances, 42 of which were starts. He's been mostly used as a reliever in the Majors.
"I'm looking forward to it ... it's exciting," Cashner said Thursday. "I'm excited about the opportunity to do something I've wanted to do. I didn't think it would be this year."
Right-hander Michael Fiers gets the call for the Brewers. The 26-year-old Fiers makes the third start of his young career. He is 1-1 with a 3.75 ERA this season.
After allowing one run through seven innings in his Major League debut against the Dodgers, Fiers had a tougher time in his second start versus Pittsburgh. He gave up four runs on eight hits in five innings.
"I threw the ball well," Fiers said after the game. "The mistakes I made, they were hit hard. And in this game, good hitters, they're going to capitalize on those mistakes."
Padres: Thayer reflects on closing
• With Huston Street back from the disabled list, Dale Thayer was removed from his closing duties. As unexpected as it was for Thayer, he excelled in the pressure-packed role. He was 5-for-5 in save chances and allowed only six hits.
"It was fun," he said. "I wasn't expecting to be put in that position, but it's pretty much the same. When I was out there for an inning, it was just about going out there and getting three outs."
• Outfielder Will Venable is still recovering from a tight right oblique, but is getting much closer to a return. He hit off a tee in Milwaukee and went through his regular routine.
"I can do everything," he said. "I just got to see how far I can go without putting myself at risk for doing something worse to it. That's really the only issue right now."
Brewers: Coulter and Roache agree to terms
• Catcher Clint Coulter and outfielder Victor Roache, the Brewers two first-round picks in the 2012 First-Year Player Draft, agreed to terms five days after being drafted. Coulter received a $1.675 million bonus and Roache signed for $1.525 million.
"These are two players who have only taken a few days to sign their contracts," general manager Doug Melvin said. "They're both very anxious."
• Second baseman Rickie Weeks is 1-for-18 in his last five games. He is batting .157 for the season, the lowest average in the Majors among qualifiers. His 71 strikeouts also pace the big leagues.
• With the National League having two extra teams, the Padres and Brewers were the only two teams left out of Interleague Play this weekend. However, the Padres next series is against the Mariners, while the Brewers play the Royals.