Toronto Raptors forward Pascal Siakam is doubtful for Sunday's NBA playoff clash against the Philadelphia 76ers.

A right calf contusion means the Raptors could be without Siakam for Game 4 of the Eastern Conference semi-finals.

The Raptors trail the 76ers 2-1 in the series and Siakam told reporters on Saturday: "It's weird.

"I feel like the team can always count on me to be out there every single night, but things happen."

The injury is believed to have occurred during the fourth quarter of Thursday's Game 3, when Siakam was called for a flagrant foul after he stuck his right leg out in the direction of Joel Embiid.

The two made contact and Embiid's knee appeared to hit Siakam's calf. The Raptors star then left the game and did not return. 

If Siakam is ruled out for Game 4, it will be a big loss for the Raptors as they try to bounce back from Thursday's 116-95 loss in Philadelphia. 

Siakam, 25, has made significant contributions on the offensive side through the playoffs, averaging 22.9 points through eight games.

He is Toronto's second-leading scorer behind Kawhi Leonard, who has averaged 31.5 points per game.