Mayor Thomas M. Menino’s diabetes, disclosed during a news conference Monday when he was transferred to a rehabilitation hospital, was probably triggered by the multiple medical problems he had when he began a monthlong stay at Brigham and Women’s Hospital in October, one of his doctors said Tuesday.

Dr. Charles Morris, an internist at the Brigham who helped treat the mayor, said via e-mail that the mayor entered the hospital with an elevated blood sugar level that he believes was exacerbated by the “stress of ­being sick.” High blood sugar is an indicator of diabetes.