NEW YORK (WFAN/AP) — Yankees reliever Joba Chamberlain has undergone an MRI exam for a strained muscle near the rib cage.

Manager Joe Girardi on Tuesday said doctors were examining the results of Monday’s test on the left side of his upper body. He said the right-hander will not pitch for at least the next few days.

“They want to go slow,” Girardi said. “Anything dealing with an oblique, there’s concern.”

Chamberlain had treatment on the Yankees’ off day on Tuesday.

Pitcher Sergio Mitre is expected to throw off a bullpen mound on Wednesday. He was scratched from his scheduled start Monday night against Boston because of a sore left upper body muscle.

Bartolo Colon, competing with Freddy Garcia, Ivan Nova and Mitre for one of two open spots in the rotation behind CC Sabathia, Phil Hughes and A.J. Burnett, allowed four hits and struck out seven in six scoreless innings of a simulated game.

“As the time goes by, I feel better and better,” Colon said through a translator. “Everything is good. I need to continue to work, and made the decision tough.”

Colon threw 56 of 79 pitches for strikes.

“He’s throwing a ton of quality pitches,” Girardi said.

The final decision on the rotation openings may not take place until near the end of spring training.

“They’re making it difficult,” Girardi said. “It’s probably going to come down to the last two weeks.”

Sabathia also took part in the simulated game, giving up two hits, two walks and striking four over 6 1-3 shutout innings against a group of Yankees’ minor leaguers. The expected opening day starter threw 82 pitches.

“My pitches are coming along,” Sabathia said. “My fastball command has been pretty good. I’m feeling pretty good.”

Notes: RHP Mark Prior (illness) is feeling better and played catch in the outfield. … C Kyle Higashioka was sent to th minor league camp.

Who’s your favorite to land New York’s last two rotation spots? Let us know in the comments below…

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