Aaron Nola's first full-major league season may be finished because of an elbow strain and all indications point to his being replaced in the starting rotation by top pitching prospect Jake Thompson.

The Phillies placed Nola on the 15-day disabled with a right elbow strain Wednesday before their game against San Francisco. He said he felt the discomfort during his last start, when he allowed three runs in five innings on July 28 and his fastball registered its lowest velocity of the season.

Nola told the team's trainers three days later as they boarded the bus to Atlanta's airport. He had an MRI exam on Wednesday morning, which Nola said did not reveal ligament damage but just a "mild strain." It will be a challenge for Nola to return as there are just two months left in the season and the Phillies will be wary about rushing him back.

"If we shut him down for two or three weeks, by the time he builds himself back up, you're in the middle of September," manager Pete Mackanin said. "So that very well might be the case. He might be shut down for the season. That will be determined after his two weeks on the disabled list."

Nola said he initially thought the pain he felt was nothing to worry about. But then he felt it again on Sunday morning after throwing a bullpen session, prompting him to tell the team about his elbow.

"It's not something I thought would ever happen," Nola said. "But I'm going to stay positive and try to get through this as quick as I possibly can."

The Phillies replaced Nola with Phil Klein, a righthander who was claimed off waivers from Texas in June. His time in the majors has been spent mostly as a reliever and he is likely with the Phillies for only one start.

Mackanin said it is a "good, solid guess" that Thompson will replace Klein. Thompson was unable to pitch Wednesday because he pitched Sunday for triple-A Lehigh Valley. He is scheduled to pitch Friday for the IronPigs and has a 1.21 ERA in his last 11 starts. The 22-year-old has proved that he is ready for a shot at the majors, but the Phillies needed to wait for an opening in the rotation.

Nola's trip to the disabled list could bring finality to a trying season. He has a 9.82 ERA in his last eight starts and battled through what the Phillies called a "dead-arm period." He was shut down before the all-star break to give him an added respite but said Wednesday that he did not feel any discomfort until his last start. Nola's season has been anything but easy. He is 6-9 with a 4.78 ERA.

"I hope it's not the end," Nola said. "I'm going to try everything I can to get back at the end of the year. Try not to rush anything and do the rehab the correct way and do what I need to do. I feel like I can build on some of the pains of this year, especially at the end of the first half and when I came back. Just try to build on those things and learn from them."

Extra bases

Michael Mariot joined the team from Lehigh Valley as Jeanmar Gomez was placed on paternity leave. Gomez' wife, Luisa, was induced into labor on Wednesday. Mackanin said Gomez expects to return to the team on Thursday.… Vince Velasquez will start on Thursday afternoon against San Francisco lefthander Matt Moore (7-7, 4.08 ERA).