When soreness in Cashner's elbow popped up for a second time this month, the team decided to stick him on the 15-day disabled list on Saturday and get an MRI on the elbow, which will occur Monday in San Diego.
Cashner, who was scheduled to start Sunday against the Rockies, was upbeat and optimistic that this setback isn't anything catastrophic.
"I think it just has some inflammation in it," he said. "Hopefully it's not more than 15 days. I think there was some extra soreness this time, but I'm not worried at all about my ligament. I have been cutting my fastball loose with no pain."
Rookie Donn Roach, who has been a long reliever out of the bullpen, will make his first big league start in the series finale on Sunday. The Padres recalled reliever Kevin Quackenbush from Triple-A El Paso to give them an extra bullpen arm if needed.
Cashner, who ranks eighth in the National League with a 2.35 ERA, is coming off a start on Tuesday against the Reds in which he allowed one run over seven innings, with one walk and six strikeouts. He threw a side session in Cincinnati on Thursday and had soreness Friday.
It was similar to the soreness he experienced after a start against the Royals on May 7, according to San Diego general manager Josh Byrnes.
"More than anything, we wanted to err on the side of caution with the soreness he has had off and on," Black said. "He came in and was quite honest and we should really consider this because I want to nip this in the bud instead of trying to push something."
Cashner is 2-5 and opponents are hitting .235 against him this season. According to FanGraphs, Cashner has leaned more on his fastball this season (72.8 percent, up from 63.4 percent in 2013) and slider (18 percent, up from 14.4 percent a year ago).
In that start against the Reds, Cashner allowed three hits and one run in the first inning, but settled down thereafter. He was still throwing 94-95 mph in his last inning of work.
Earlier this season, Cashner nearly became the first Padres pitcher to throw a no-hitter, as he allowed one hit in a shutout of the Tigers on April 11. To date, he has only surpassed the 100-pitch mark twice, and hasn't thrown more than 108 pitches in any single start.
"We felt it was the right thing to do. He'll have an MRI on Monday and that will tell us more," Byrnes said. "We're cautiously optimistic that rest will knock this out."
Losing Cashner for any length of time will be a blow to a starting rotation that has maintained all five of its starters since Opening Day -- as the Padres are one of only three teams to do so. The others are the Red Sox and Brewers.
Heading into Saturday's game, Padres starting pitchers had the eighth-lowest ERA (3.42) in the Major Leagues.
Black is hopeful, as is Cashner, that this setback won't keep him on the DL longer than the 15-day period, which officially began on May 15.
"I like the fact that Cash is optimistic about this. As a player, you know when something is wrong. He feels pretty good about his situation and with a little bit of rest he'll be fine," Black said.