By Monday night, the Orioles hadn't announced their starting pitcher for this afternoon's series finale against the Detroit Tigers.

Now we know why.

The Orioles will recall right-handed pitching prospect Kevin Gausman to start the 12:35 p.m. game at Camden Yards, the club announced Tuesday. After Tuesday's game, the Orioles optioned right-hander Preston Guilmet to Triple-A Norfolk to clear a roster spot.

Gausman was informed of his call-up when Norfolk was making its connecting flight in Atlanta after a road trip in Indianapolis, and he drove to Baltimore after arriving in Virginia.

It's unclear how long Gausman will remain with the club, but his call-up is another twist in what has been an up-and down season for the Orioles' 2012 first-round pick.

Gausman, 23, kept opponents off the board for three of his first five starts for Norfolk, compiling an 0-1 record and a 2.53 ERA, before he woke up last month with a pain in his chest. He said doctors told him it could have been a fractured rib or an intercostal strain, making him the unlikely patient who welcomed his eventual pneumonia diagnosis.

“When the doctor told me, I was happy,” Gausman said. “He was like, ‘That's probably the first time anyone has every been happy to have that.'”

Gausman returned from the disabled list Saturday to lower his season ERA to 2.08 with 4 2/3 scoreless innings against Indianapolis. He allowed two hits and three walks while striking out six batters.

Gausman said he feels good about his pitches now, but he said the season has been uneven for him from the start.

“It's been kind of crazy,” Gausman said. “I started off the season sick, and had to grind through two starts where I wasn't feeling very good, but that's just part of baseball, especially being a starting pitcher.”

Gausman was 3-5 with a 5.66 ERA in 20 appearances with the Orioles last season, including 0-3 with a 7.66 ERA in five starts. In his third start last year, Gausman allowed one run, five hits and no walks in six innings in a no-decision against the Tigers on June 2.

Gausman said he would draw from that experience, but he said he also would have to prepare for the new faces in the Tigers lineup.

“It's a completely different lineup than what they had last year,” Gausman said. “I think [Prince] Fielder was kind of a big part of that lineup, obviously, but [Ian] Kinsler is obviously a great hitter, too. I've never pitched against him, so I'm going to kind of do my research.”

Gausman has been on a pitch limit with Norfolk, and he will start on three days' rest today, but he said he feels as if he could throw 90 to 100 pitches in the game.

Manager Buck Showalter said the game situation and not the number of pitches Gausman throws will dictate the length of his start.

Left-hander Wei-Yin Chen, who originally was scheduled to pitch today, will start the series opener Thursday night on the road against the Kansas City Royals.

This season, heading into Tuesday, the Tigers are the best-hitting team in the American League against left-handers (.293 batting average, with the second-highest on-base-plus slugging percentage at .809), while the Royals have the second-worst OPS versus lefties (.624) in the league.

Additionally, Chen has pitched much better in his career with five days' rest (3.97 ERA) than with four days' rest (4.47).

Gonzalez to bullpen, at least for now

The rotation changes have pushed right-hander Miguel Gonzalez to the bullpen, at least temporarily.