Chicago, IL -- (Sports Network) - Chicago Cubs pitcher Carlos Zambrano was diagnosed with rotator cuff tendinitis in his right shoulder Thursday.

Already expected to miss his next scheduled start Sunday against Cincinnati, Zambrano will likely take the mound September 14 at Houston after an MRI revealed the hurler needed anti-inflammatory medication and a few days rest.

Zambrano left after five innings of Tuesday's 9-7, 11-inning loss to Houston due to an apparent relapse of a tired arm. Zambrano was scratched from his Sunday afternoon start against Philadelphia because of the problem.

On Tuesday, he lasted 86 pitches before telling Cubs pitching coach Larry Rothschild he didn't feel well, then left the game.

The 27-year-old right-hander is 13-5 in 27 starts this season with a 3.58 ERA.