Abdel Nader sustained a concussion Friday in a scrimmage against the Celtics, the Thunder announced Saturday.
Nader has been placed in the NBA's concussion protocol. According to NBA concussion policy, Nader will proceed through a series of steps to ensure "symptom-free behavior" before he resumes basketball activities.
There is no timetable for Nader's return.
Nader suffered the injury in the final minutes of the scrimmage, when his head banged against the court during a fall.
The 26-year-old wing, in his second season with the Thunder, is averaging 6.0 points and 1.9 rebounds in 15.8 minutes per game.