A pneumothorax or as it is known to most people "collapsed lung"
Via ACC Now:
As a result of the back bruise he sustained in Sunday's game at Georgia Tech, UNC basketball player Leslie McDonald also is dealing with a pneumothorax, which team spokesman Steve Kirschner -- after talking to the team trainer -- described as occurring when air gets trapped outside the lung, but is pushing against the lung.
McDonald took a hard fall and may have taken an elbow to the back or ribs during the fall. Obviously this type of injury would make playing basketball difficult. The question is how quickly McDonald can bounce back. If there was ever a week to have an injury this is the week. UNC does not play again until next Wednesday in Miami.
Trivia question: Name the other Tar Heel to suffer a collapsed lung via an injury on the court. Bonus points if you can tell me when it happened and how(Hint: the injury occurred during a very significant game in Dean Dome history.)