Foster played only five minutes against Wichita State before suffering the left knee injury on a drive to the basket, and missed the Mustangs' game against Tulane on Saturday. SMU coach Tim Jankovich called it a knee sprain prior to Saturday's game, but Foster underwent an MRI on Monday.
Foster, a 6-foot-6 junior, was SMU's second-leading scorer and leading rebounder, averaging 13.2 points and 5.9 rebounds.
Junior guard Jahmal McMurray saw an uptick in minutes the past two games without Foster, averaging 14.5 points.
SMU (14-6, 4-3 AAC) plays at Connecticut on Thursday.
The news was first reported by 247Sports' SMU affiliate.