(CNN)Milwaukee Bucks star Giannis Antetokounmpo limped off injured during his side's 110-88 defeat by the Atlanta Hawks on Tuesday.
The two-time NBA MVP was forced off after appearing to hyperextend his left knee following an awkward landing in the third quarter of the game.
He was helped back into the locker room and returned to watch from the sidelines.
"It's not good," said Bucks forward P.J. Tucker. "It's not good losing anybody on your team and losing your best player stinks."
It's unclear whether Antetokounmpo will be available for Game Five with the Eastern Conference finals clash finally poised at 2-2. The next game in the series is set for Milwaukee on Thursday.
"We'll take everything as it comes. We'll evaluate it. We've got a heck of a team, a heck of a roster," said Bucks coach Mike Budenholzer.
'Sending my thoughts'
Lou Williams, who started a playoff game for the first time in his 16-year NBA career, led the scoring with 21 points for Atlanta, with Bogdan Bogdanovic adding another 20 points.
All together, six Atlanta players finished in double digits as they took full advantage of Antetokounmpo's absence.
Williams said he only found out an hour before tip-off that he would be playing in place of his injured teammate Trae Young.
Young was among those to send his good wishes to Antetokounmpo after watching his side win the game.
"Sending my thoughts & prayers to [Antetokounmpo]," he wrote on Twitter.