(Reuters) - NBA Commissioner David Stern has vowed to punish the San Antonio Spurs for sending Tim Duncan, Tony Parker, Manu Ginobili and Danny Green home early rather than play in Miami on Thursday against NBA champion Heat.

With the second-placed Spurs (13-3) set to take on Southwest Division leading Memphis (11-2) in San Antonio on Saturday, coach Gregg Popovich decided his group of veterans could use an extra day of rest at home after their hectic road stretch.

Stern lashed out at the move, which came before the Spurs' nationally televised marquee clash against the Southeast leading Miami Heat (10-3).

"I apologize to all NBA fans," Stern said in a statement. "This was an unacceptable decision by the San Antonio Spurs and substantial sanctions will be forthcoming."

The Spurs, who had won the first five games of their six-game road trip ending in Miami, were left with just nine active players for the game against the Heat.

(Reporting by Larry Fine, Editing by Peter Rutherford)