The injury occurred when Calderon was defending Tony Parker's drive to the basket with 8 minutes, 35 seconds left in the third quarter. As Calderon leaned in to go for the ball, his nose collided with Parker's left shoulder.
"It is what it is," Calderon said of the injury.
Calderon subbed out of the game during the next dead ball, which didn't come until the 8:13 mark of the period.
Mavs head athletic trainer Casey Smith looked at Calderon, but it was quite evident that a serious injury had occurred as blood came pouring out of the point guard's nose. Calderon went to the locker room to get X-rays on the nose, which ultimately revealed the break.
"It was bad luck that he got hit when he did because he was playing so well on both ends," Mavs coach Rick Carlisle said. "He was hitting shots. Sometimes, these things happen."
Despite the injury, Calderon returned to the bench and came back out on the floor at the 4:22 mark of the period. After returning, Calderon scored three points, coming off a crucial 3-point basket that got the Mavs back to within one with 10:16 to go in the fourth.
"It was a little tough to breathe in the second half," said Calderon, who had 12 points on 5-of-9 shooting, six assists and five rebounds in the Game 6 victory. "That's why I asked for a sub, because I couldn't breathe out there.
"I hope I'm better in Game 7. I think we were trying to stop the bleeding, so there was a lot of stuff up my nose. I think it was that more than anything else with the breathing."
With the team not scheduled to practice Saturday and traveling to San Antonio, it will be up to the team's medical staff to determine if Calderon will need to wear a supportive mask in Sunday's crucial Game 7.
"We'll see the doctors, and we'll go from there," Calderon said.