David Lee tore his right hip flexor in Saturday's loss by the Golden State Warriors to the Denver Nuggets and is out for the season.
While x-rays on Saturday were negative, an MRI on Sunday revealed the complete Grade 3 tear.
Lee was playing his first game in the NBA Playoffs after being in the league since 2005.
The Warriors are in their first postseason since 2007 and trail the Nuggets 1-0.