During the third quarter, Allen was positioning himself for an offensive rebound and fell awkwardly after gaining possession.
The 21-year-old remained on the floor for a bit before leaving the game.
A member of the Nets' medical staff accompanied him to the locker room. He later returned to Brooklyn's bench for the remainder of the contest.
Allen entered the game averaging 16.8 points, 9.8 boards, and 2.3 blocks across four summer league appearances. He finished with 15 points, 14 boards, and two blocks against the Timberwolves.
Allen has been the Nets' primary starting center over the past two seasons, but he could receive some competition in 2019-20 from newly signed DeAndre Jordan.