When Al Horford left Thursday night's game against Cleveland with a shoulder injury, it didn't look good. And a league source says the Hawks are bracing for the worst: the possibility that Horford tore his right pectoral muscle -- an injury that he suffered to his other pec two seasons ago.

The team is awaiting MRI results, but if they confirm the worst fears, Horford would stand to miss significant time -- a devastating blow to the only team in the East besides Indiana and Miami that is over .500.

Horford, 27, left Thursday night's game in Cleveland after reaching for a steal against the Cavs' Anderson Varejao during the first overtime. He walked off the floor grasping his right chest and looking under his arm -- as if something were missing.

He suffered a torn left pectoral muscle in January 2012, only 11 games into the lockout-shortened season. He returned for three playoff games in May, almost four months later.

Horford had been enjoying one of the best seasons of his seven-year career, averaging 18.6 points and 8.4 rebounds while shooting 57 percent from the field in 29 games.