After the game the Cubs announced that the MRI/Arthrogram performed on Carlos Zambrano's right pitching shoulder showed absolutely NO structural damage. Specifically there was no evidence of a labrum injury or rotator cuff tear. There was some inflammation in the back of the shoulder which probably refers to the infraspinatus muscle, hence the Tribune reporting the test showed a minor shoulder strain.
The infraspinatus is the posterior of the four muscles that make up the rotator cuff. Cuff tears are mostly synonymous for a tear in the supraspinatus tendon which is the superior muscle and tendon. The muscle in front is the subscapularis and the teres minor is posterior below the infraspinatus. A mild muscle strain implies some inflammation but no significant stretch or tear of the muscle fibers. So with no structural damage and a collective sigh from all places Cub Blue, the conservative thing is to let Zambrano's shoulder rest for two starts. Supposedly they discussed this with Z and they wanted to know if he should miss only one start (vs. Baltimore) or two starts (at US Comisk-ular). Rumor has it that when Zambrano was told he would not bat in an AL team home park he opted to miss two starts.