SAN DIEGO -- Padres starter Cory Luebke said an MRI showed possible damage to the ulnar collateral ligament in his left elbow, but the exact injury is unknown.

"Until some of the swelling gets out of there, we won't be able to get a real good look at it," Luebke said Saturday.

Luebke could face surgery, but he and the Padres remain in an evaluation process regarding his elbow injury. He underwent an MRI on Wednesday that showed swelling and a little fluid. He went on the disabled list Wednesday, retroactive to April 28.

"We were hoping that [the flexor tendon] was the main part of the injury. It's a little less severe," Luebke said. "We did some X-rays and it showed something a little different. We still don't know exactly what's going on. The symptoms are all kind of pointing a certain way [to possible ligament damage]."

Luebke said he had previously never missed a start during his entire career.

"One of the things we enjoy doing is playing and being out there every fifth day, and to know there's a chance I might not be able to do that for a while is kind of disheartening," Luebke said. "But that's part of the game. I don't have to look around too far in this clubhouse to see some guys who are going through some stuff, too. You can't really feel too sorry for yourself. You have to do what you got to do."

If Luebke needs Tommy John surgery, he would likely be out for a year.

"A lot of worse things have happened. If it does come to that, the success rate, they're getting real good at it," Luebke said.

Manager Bud Black said Luebke continues to rest the elbow and receive treatment.

"As of now, [there's] no definitive plan as far as a rehab situation. [We're] still plotting a course of action," Black said.

Luebke joined fellow starters Dustin Moseley (shoulder) and Tim Stauffer (elbow) on the disabled list. Moseley is expected to be out for the season following shoulder surgery. Stauffer is expected to make one more rehabilitation start on Wednesday with either high Class A Lake Elsinore or Triple-A Tucson in New Orleans before he comes off the disabled list.

Luebke first felt discomfort in his elbow in the fourth inning of his last start against the Giants.

Luebke said his MRI exams during Spring Training revealed good results. In March, Luebke signed a contract extension that will guarantee him $12 million and could keep him with the Padres through 2017. He is 3-1 with a 2.61 ERA.

"I've been lucky," Luebke said. "Twenty-seven years of playing ball, I never really had to miss a start or miss anything."

Stauffer to make third rehab start Wednesday

SAN DIEGO -- Padres starter Tim Stauffer is expected to make a third and possibly final rehabilitation appearance on Wednesday.

Stauffer will pitch for either Class A Lake Elsinore, which will be playing at home, or Triple-A Tucson, which will be playing in New Orleans, Padres manager Bud Black said.

Stauffer was encouraged by his last outing. He allowed a run and six hits in five innings for Tucson on Friday. He struck out one and walked none. He threw 70 pitches, 50 for strikes.

"It was good getting the work in and getting up and down five times, getting in a competitive atmosphere again," Stauffer said. "I felt pretty sharp for the most part. I was able to throw strikes and kept the ball down a little better this time."

Stauffer went on the disabled list April 5, retroactive to April 4, for a strained right elbow. In his first rehab outing, he allowed two runs and six hits, struck out three and walked none in 3 2/3 innings with Lake Elsinore.

"I was definitely happier with the pitches I was making and repeating my delivery I think a lot better [Friday]," Stauffer said.

"[The slider] was better," Stauffer added. "Fastball command was better. Everything was a little bit lower than the previous start."

Mikolas called up for first time, makes debut

SAN DIEGO -- When pitcher Miles Mikolas' phone rang and woke him at 8 a.m. PT on Saturday, he wondered if he had missed the team bus to a Double-A game.

Instead, Mikolas received the news he was headed to the Major Leagues.

The Padres selected Mikolas from Double-A San Antonio on Saturday to replace closer Huston Street, who went on the 15-day disabled list for a strained right lat. To make room for Mikolas on the 40-man roster, the Padres moved infielder Logan Forsythe to the 60-day disabled list.

Mikolas, who made his debut in the ninth inning of Saturday night's 4-1 loss, was 1-1 with a 2.92 ERA in Double-A. He allowed a solo homer to the first batter he faced, Giancarlo Stanton. He also struck out two and walked one.

"This spring, he threw the ball well," San Diego manager Bud Black said. "I think that continued on there in San Antonio. Of all the guys that we looked at, he was the guy that our Minor League people said, 'He's the guy.'"

Mikolas caught a flight out of San Antonio and arrived at Petco Park shortly before 2 p.m., roughly 3 1/2 hours before the team's first pitch against the Marlins.

"I had a little time to get ready," Mikolas said. "I had a small bag packed for our trip to Corpus [for a Double-A game]. I had to unpack and pack my big bag."

Mikolas spent much of Spring Training with the big league team, and he's been teammates with some of the younger players.

"It's easier knowing the guys a little bit so you don't just show up and you don't know anybody at all," Mikolas said. "There are a lot of young guys up here, which makes it a little easier to make the transition."