MMA Weekly talks to Greg Nelson, Lesnar's head coach:

Greg Nelson, a two-time cancer survivor who leads Lesnar's fight camps along with Erik Paulson and Marty Morgan, said the UFC heavyweight champ is still recovering from a severe case of diverticulitis (an infection in the digestive tract), but wants to get back into the gym.

Heavy.com adds more:

Heavy.com has learned from UFC sources that the company is internally targeting July as a potential return date for Lesnar and that the Lesnar/Carwin bout could headline the UFC's initial foray into Massachusetts. A July date has been secured with the TD Garden in Boston for a card that will serve as the centerpiece of the UFC's summer 2010 schedule.

Please note that much of the information that came from Dana White regarding Lesnar's health has not been borne out. Nelson confirms to MMA Weekly that Lesnar never went to the Mayo Clinic for instance.