Mellusi, who leads Wisconsin with 815 rush yards on 173 carries, left last week's win over Rutgers with the injury to his left leg. He initially was listed as questionable for Saturday's game against Northwestern, although Chryst on Monday said doctors were still "waiting to find out exactly what it is."
Chryst on Thursday did not specify Mellusi's injury but said the junior, who transferred to Wisconsin from Clemson, is not expected to return for spring practice. Mellusi has started the first nine games for No. 18 Wisconsin.
Mellusi's injury means freshman Braelon Allen will see an even bigger role after blossoming during Wisconsin's five-game win streak. Allen has five consecutive 100-yard rushing performances, becoming the first Wisconsin freshman to do so since Anthony Davis in 2001. He averages 7.1 yards per carry, which ranks fifth nationally among players with at least 90 carries.