Knicks forward Amar'e Stoudemire underwent an MRI on his back Wednesday after missing the second half of the Game 2 playoff loss to the Celtics with back spasms.
The MRI confirmed a pulled muscle, and Stoudemire is listed as day-to-day with the injury.
Stoudemire experienced the spasms after trying to dunk during warm-ups and managed to play 17 minutes before exiting with 3:22 left in the first half of the Knicks' 96-93 loss.
The All-Star power forward, who had 28 points and 11 rebounds in the Knicks' Game 1 loss, was confident after the game Tuesday night that he would be able to return for Game 3 on Friday night at Madison Square Garden.
"I should be ready. We'll see how it goes [Wednesday] and next day, but I'm pretty sure — I'm hoping — I'll be ready Friday."
He said the spasms were too painful to play through, forcing the already shorthanded Knicks to rely heavily on Carmelo Anthony, who responded with a heroic 42 points and 17 rebounds.
"I couldn't hardly move. I was trying to play through it," Stoudemire said. "Once I felt that sharp pain, I couldn't take it."
Meanwhile, point guard Chauncey Billups, who missed Game 2 with a strained left knee, also had an MRI exam on Wednesday.
Billups' test confirmed a strained tendon, which forced him to miss Game 2 after he was hurt on a drive to the basket near the end of the series opener. Billups is listed as doubtful for Game 3.
The Celtics lead the best-of-seven first-round series 2-0. The Knicks are still looking for their first playoff win since April 29, 2001.