Fisher got hurt Tuesday, the second time in less than six months he injured a knee in practice. He had surgery after a meniscus tear in his left knee in early August.
The sophomore guard missed the team's trip to Australia after the previous surgery, but was ready for the regular season. He averaged 12.1 points and was fifth in the Big 12 with 5.4 assists while playing the first 17 games. He had a career-high 22 points in an overtime loss Saturday at No. 4 Oklahoma, and he made 11 of 20 shots from 3-point range his last four games.
Fisher will need three to four months of recovery.
"I feel bad for him. We all feel bad for him," coach Jamie Dixon said.
Even with his knee locked in a bent position and having to use crutches, Fisher attended TCU's 96-73 home win over Iowa State on Wednesday night. He sat in a chair near the TCU bench.