PHILADELPHIA -- Toronto Raptors forward Pascal Siakam suffered a right calf contusion, and has been listed as doubtful for Game 4 of the Raptors' conference semifinals series against the Philadelphia 76ers on Sunday.

Siakam said on Saturday he hurt the calf in the Raptors' 116-95 loss at Philadelphia in Game 3 on Thursday, but couldn't recall precisely when the injury occurred.

"I don't know exactly when it happened, but after the game I was just like really sore," Siakam said. "I think it calmed down a little bit, then I felt worse."

Siakam hasn't been able to put the leg through much physical activity since Thursday. The calf has been undergoing treatment, including ice as well as light movement therapy, he said.

A favorite to win the NBA's Most Improved Player award, Siakam has emerged as one of the Raptors' most consistent offensive producers behind Kawhi Leonard this postseason. In eight postseason games this spring, Siakam has averaged 22.9 points, 7.4 rebounds and 2.5 assists, with an effective field goal percentage of 56.9. Siakam is also a versatile defender who has guarded all five positions for the Raptors at various junctures over the past two postseasons.

Siakam's absence would challenge the Raptors because the team is already without reserve forward OG Anunoby, who underwent an emergency appendectomy just prior to the start of the playoffs.

"With the OG out, it's not the ideal position for us," said Raptors coach Nick Nurse. "We're a little thin there."

Each scenario presents a different complication for Toronto. Nurse suggested Raptors backup guard Fred VanVleet as one option, noting the team had enjoyed success with pace and ball movement when VanVleet has played as part of a three-guard lineup. In 56 minutes on the floor with the starting backcourt and Leonard, lineups featuring VanVleet averaged 116.7 points per 100 possessions, with a net rating of plus-46.8.

Yet replacing Siakam with a perimeter player would put the Raptors at a greater size disadvantage against a Philadelphia team that features exceptional length and has hurt Toronto on the offensive glass.

"Size has been a problem," Nurse said. "We knew coming into the series that they would have size at a lot of positions."

The Raptors could also opt to start backup big man Serge Ibaka, who has struggled in the series. Nurse also suggested as another possibility 6-foot-7 swingman Patrick McCaw, who has seen limited time on the floor since returning from a right thumb injury. Introducing McCaw into the starting lineup would enable the Raptors to preserve their current rotation, Nurse said.

With the Raptors trailing 2-1 in the series and now potentially without their second-most prolific scorer, Raptors guard Kyle Lowry said that it was imperative for the rest of the team to compensate in an effort to help leading scorer Kawhi Leonard.

"Kawhi has been unbelievable in the playoffs, Pascal's been unbelievable in the playoffs," Lowry said on Saturday. "As other players around those guys we need to step up in general, make some shots, be more aggressive, draw some more fouls, try to do some more things to help relieve the little bit of the scoring burden off of them."