Phoenix Mercury center Brittney Griner missed Saturday's game against defending champion Indiana due to a left knee sprain.
Griner dressed for the game and participated in warm-ups but was ruled out for the game.
The former Baylor star, selected No. 1 overall by Phoenix in this year's WNBA draft, was averaging team highs of 16.7 points, 6.7 rebounds and 2.3 blocks in her first three games.
The team did not disclose how or when the injury occurred.
Asked how long Griner would be out, Phoenix coach Corey Gaines said: "It doesn't look bad, but I don't really know."
The Mercury began the day 0-3 and last in the Western Conference.