The Philadelphia 76ers fear All-Star center Andrew Bynum might have done additional damage to his knees while bowling, according to sources close to the situation.

Multiple sources told ESPN on Saturday that Bynum suffered an unspecified injury this month while bowling. On Friday, Bynum revealed that — on top of the issues with his right knee that could keep him sidelined until January — he also had suffered a “setback” with his left knee.

There are several activities that are prohibited in standard NBA player contracts, but bowling is not one of them. Bynum is known to enjoy bowling.

via Brian Windhorst and Chris Broussard of ESPN