Alex Poythress tore the ACL in his left knee during Thursday's practice and will miss the rest of the season for top-ranked Kentucky, the school announced Friday morning.
A date for surgery has not been set, but recovery typically takes six to eight months.
Poythress' injury causes a major shakeup to John Calipari's two-platoon system, where the 6-foot-8 junior was averaging 5.5 points and 3.8 rebounds in 20 minutes of action.