Celtics' Kristaps Porzingis out for Game 3 of NBA Finals vs. Mavs - ESPN

DALLAS — The Boston Celtics have ruled out center Kristaps Porzingis for Game 3 of the NBA Finals against the Dallas Mavericks on Wednesday.

Porzingis was diagnosed with a torn medial retinaculum allowing dislocation of the posterior tibialis tendon in his left leg Tuesday afternoon — an injury the team said in its release announcing it was a «rare» one and one Celtics coach Joe Mazzulla said was a serious one.

Mazzulla also said Porzingis' status after the injury, which the team said came at the 3:27 mark of the third quarter in Game 2, would be determined by the medical team, and not Porzingis, to take any pressure on him playing out of his hands.

Mazzulla said before Game 3 that Porzingis remains day-to-day moving forward. He added that Porzingis went through some testing with the medical team to determine whether he could play, and after seeing Porzingis go through that, it was determined Porzingis couldn't play and he was ruled out for Wednesday's game.

Porzingis was seen walking around with a sleeve on his left leg and a brace on his left ankle both Tuesday and again at shootaround Wednesday, and without a noticeable limp either time. But Boston ruled him out about an hour and 45 minutes before tipoff Wednesday, leaving the Celtics without their best rim protector and another elite shooter as they try to take a 3-0 lead in this series.

The Celtics were plus-25 in the 44 minutes Boston had Porzingis on the court over the first two games of the series and were even in the 52 minutes he was on the bench.

Al Horford will remain in the starting lineup Wednesday, and Boston could turn to either Luke Kornet, Xavier Tillman or Oshae Brissett to fill in for Porzingis' minutes off the bench.