Tigers coach Josh Pastner says Witherspoon was undergoing arthroscopic surgery Friday on his right knee meniscus.
Witherspoon will undergo rehabilitation during the next five weeks. He could return Jan. 15 against Marshall.
Witherspoon, a junior, was hurt in the Nov. 17 Northwestern State game, but kept playing. Pastner had limited Witherspoon's practice time the past 2½ weeks.
Witherspoon is averaging 13 points per game and 4.6 rebounds per game for the 7-1 Tigers (No. 14 ESPN/USA Today; No. 13 AP).