Fisher is scheduled to have surgery Thursday. He suffered the injury during Tuesday's practice, marking the second time in about six months he hurt a knee in practice.
Fisher tore the meniscus in his left knee when the team was preparing to go to Australia in August, a trip Fisher missed for surgery.
Fisher is the starting point guard for the Horned Frogs, averaging 12.3 points and 5.4 assists. Over his past four games, Fisher has put up 16.3 points and 4.3 assists, including a 22-point effort in a loss to Oklahoma on Saturday.
TCU (13-4) has lost four of five in Big 12 play, after starting the season 12-0.
Without Fisher, expect guard Alex Robinson (7.4 PPG, 4.9 APG) to see more time on the ball. Jamie Dixon is also likely to use a bigger lineup that features 6-foot-5 Desmond Bane (12.1 PPG) and 6-foot-7 Kouat Noi (9.1 PPG) on the wings.
TCU hosts Iowa State on Wednesday.
Information from The Associated Press was used in this report.