The Raptors all-star was diagnosed with a torn tendon in his groin Saturday, bad news for a Raptors team that's off to its best start in franchise history.
DeRozan injured his groin at the 8:23 mark of the third quarter of Friday's 106-102 loss to the Dallas Mavericks.
DeRozan, who remained on the court for several minutes before being helped to the dressing room, was originally diagnosed as having a strained left groin.
He went for further diagnostic testing, which revealed the torn left adductor longus tendon.
The Raptors say there is no timetable for his return to basketball activity.
DeRozan, who's missed just 10 games due to injury over six NBA seasons, has averaged a team-high 19.4 points, 4.2 rebounds and a team-best 33.6 minutes in 16 games this season, and has led the team in scoring eight times.
The Raptors (13-3) saw their six-game winning streak end with Friday night's loss. They return to action Sunday when they face the Lakers in Los Angeles.