Looks like Tracy Morgan will be missing some episodes of 30 Rock after getting a kidney transplant.   Tracy got diagnosed with diabetes back in 1996. Here's the info:

Expect a huge void on TGS in March: EW has learned exclusively that Tracy Morgan—aka Tracy Jordan, the star of the show within the show, 30 Rock—will miss at least two episodes of the NBC comedy because he’s recovering from surgery. The comedian underwent a kidney transplant on or around Dec. 10 and though the surgery was successful—he was seen at a Knicks game on Friday—the writers are giving him plenty of time to recover.

via EW.com.