The Belgian powerhouse has been an influential figure since arriving on loan from Marseille but may have played his last game for City.
Van Buyten suffered the injury in training and the first match he misses is Saturday's home clash with Fulham, a game Kevin Keegan's men need to win after slipping uncomfortably close to the relegation zone.
Of course, the 26-year-old was sent off during the unlucky 2-1 defeat to Leeds United on Monday night for a professional foul on Alan Smith that led to Mark Viduka's penalty winner.
Van Buyten was due to be absent through suspension but news of his injury will come as a huge blow to Keegan, forcing him to plan his defensive thoughts without the giant centre back.
"Daniel has given us stability," Keegan told City's official website recently.
"When those balls go in there now they are coming back out.
"He has been outstanding with his own performances but obviously, when you lose, they don't get looked on in the same light as if you win."
