http://www.ufc.com/news/UFC-173-upda...+Championship&

The Ultimate Fighting Championship announced today that middleweight champion Chris Weidman has been forced to withdraw from his scheduled title defense against Lyoto Machida on May 24. Weidman suffered a knee injury that will require minor surgery and his bout with Machida has been rescheduled for Saturday, July 5. A new main event for UFC 173 on May 24 will be announced in the days to come.