Comedian Dave Chappelle has checked himself into a mental health facility in South Africa and has remained there since late April, according to a source close to the situation. The same source denies rumors of drug abuse. Other sources have also told EW that the future of Chappelle's Show the hit Comedy Central series that was entering its third season is more uncertain than the network has suggested. Comedy Central last week made a hasty announcement that the show's third season, already delayed from its planned February start, had been postponed again. The network said it remained ''optimistic'' that production could resume. The highly rated sketch series has been a huge moneymaker for Viacom, which owns Comedy Central. Its second season is about to be released on DVD, on the heels of first-season sales that made it the top-selling television DVD in history. Thanks in large part to the DVD sales, Chappelle last year netted a $50 million deal for co-writing and starring in the show. Sketches to fill about four episodes in the third season have been taped, but Chappelle's interstitial material with live audiences has not. The fate of the sketches has not been determined.