Antetokounmpo grimaced in pain under the basket late in the first half while his teammates surrounded him, but he eventually walked off the floor and straight to the locker room.
Khris Middleton started the second half of Wednesday night's game in Antetokounmpo's place. The Bucks announced he would not return.
The second-year forward from Greece was averaging 12.2 points and 5.9 rebounds going into the game against the Trail Blazers.
It has been one rough week for Milwaukee, which lost rookie Jabari Parker for the season when he tore the anterior cruciate ligament in his left knee on Monday at Phoenix.