The school announced Anigwe's status about an hour before tipoff as No. 7 seed Cal prepared to take on the 10th-seeded Cavaliers at Colonial Life Arena.
Cal coach Lindsay Gottlieb said after the game that she could not elaborate on Anigwe's condition, only that it was more important to protect a young players' health than rush her back on the court if she was not cleared to play.
Prior to the game, the school's statement said the 6-foot-4 junior had practiced fully the past two weeks but could not take part in morning shootaround and would not play in the opener.
Anigwe led Cal with 16.7 points and 8.8 rebounds this season.
Cal had won seven straight opening games in the NCAA tournament prior to Friday's loss.
Information from The Associated Press was used in this report.