Starting in place of the injured Eric Stults, who is on the 15-day disabled list, Cashner went 2 1/3 innings while giving up one earned run and two hits in a 5-2 win over the Brewers on Saturday at Miller Park. But now Black said Cashner, who last started on April 5, 2011, for the Cubs, needs to build his endurance to transition from reliever to starter.
"I think [Saturday] was a building block for future starts, which will happen," Black said. "We're going to option him out to San Antonio, and he's going to start in the middle of the week for the Double-A club and continue to build a pitch count off of what he did [Saturday]."
Black also said reliever Brad Boxberger, who has a 4.70 ERA and 35 strikeouts in 23 innings pitched for Triple-A Tucson this year, will be called up to replace Cashner on Sunday.
Although Saturday was only Cashner's second Major League start, he has started 42 games in the Minors and also was a starter in junior college. The right-hander, whose fastball touches triple digits, said going to San Antonio gives him a chance to work on the things he needs to be better at, without the pressure of pitching at the Major League level.
"I'm going to be working on my slide step a lot," Cashner said. "Really controlling the running game, throwing my offspeed, letting my offspeed work more instead of maybe guiding it in there here and there, [and] working on my breaking ball in some good counts."