ESPN News Services
It was unclear when Leonard injured the knee or when it became apparent for the Raptors.
Leonard, averaging 27 points and 7.7 rebounds, has been held out to rest periodically throughout the season as the Raptors carefully manage his minutes. He missed most of last season with a quadriceps injury.
The Raptors will also be without guard Fred VanVleet, who will miss at least three weeks with a left thumb injury.
Leonard has been in slump by his standards, but Monday he also matched his career best with eight assists.
The Raptors (42-16) have won five in a row to get back within a game of the Milwaukee Bucks for the top spot in the Eastern Conference.
Information from The Associated Press was used in this report.