On a special episode of Raw dubbed Thursday Raw Thursday, Michaels vacated the WWF Championship;[1] he explained to fans that he was informed by doctors that he had conjured a knee injury, and that he had to retire.[53] His speech was regarded as controversial, as Michaels was allegedly unwilling to lose to Bret Hart at WrestleMania 13 (since it was noted that he was going to have a rematch with Hart at WrestleMania).[6] Michaels contemplated thoughts of retirement and stated that he "had to find his smile again," which he had "lost" somewhere down the line.[6]
From the Wikipedia