(Reuters) - Boston Celtics point guard Rajon Rondo needs surgery to repair a torn anterior cruciate ligament and is expected to miss the rest of the National Basketball Association (NBA) season, the struggling team said on Sunday.

The loss of Rondo, Boston's third-leading scorer and leader in steals and assists, is a crushing blow to a Celtics team that has lost six of its last seven games and is battling for a playoff spot.

Rondo, who is averaging 13.7 points, 11.1 assists and 1.8 steals per game, was scratched from Sunday's home game against the Miami Heat two days after he suffered the injury when he hyperextended his right knee in a loss to the Atlanta Hawks.

A date for Rondo's surgery has not been determined.

The team made the announcement on its Twitter account during Boston's 100-98 double overtime win over Miami.

The Celtics (21-23) are hanging on to the eighth and final playoff spot in the 15-team Eastern Conference with 38 games left in the NBA's regular season.

(Reporting by Frank Pingue in Toronto; Editing by Mark Lamport-Stokes)