Jack Osbourne has responded angrily to a statement by NBC Entertainment Chairman Robert Greenblatt suggesting that Osbourne was dropped as a contestant on the upcoming Stars Earn Stripes reality series because the network feared that, after being diagnosed with multiple sclerosis, he may not have been able to "safely participate" in the competition. The series, Greenblatt observed, "requires Dangerous water stunts, strenuous physical activity, and uses live ammunition." In a message posted on Twitter on Monday, Osbourne said that he had already demonstrated to the producers of the show that he was up to the tasks required of the contestants. "I took part in a 16 hr challenge over 30 miles with a 40lbs ruck on my back in Jan. I had MS then. Don't tell me wot physically demanding is." He signed off "NBC said they didn't fire me over my diagnosis? Bull-F***ing-S**t#BoycottNBC." His mother, Sharon Osbourne, is already planning to do just that in support of her son, she has indicated, by refusing to return next season as a judge on NBC's America's Got Talent . Asked by the New York Post whether she might reconsider her decision, she replied, "Who know what will happen next? ... There could be a whole new crew of people at NBC tomorrow."