Stanford star forward Cameron Brink sat out the No. 1 seed Cardinal's 92-49 first-round win over No. 16 seed Sacred Heart on Friday with a non-COVID illness.
The 6-foot-4 junior is considered day-to-day, the school said. The Cardinal will face No. 8 Ole Miss on Sunday.
Brink said on Instagram that she hopes to be back soon, writing: "Not how I expected March Madness to start but cheering my girls on today - just a stomach bug & I'll be back asap."
Coach Tara VanDerveer told reporters Thursday that there was a stomach bug going around the team and that they have had "some people out" with it this week.
Brink leads Stanford in scoring (14.9 PPG) and rebounding (9.5 RPG) and earlier this season became the program's leader in blocked shots.
She had started in every contest for the Cardinal this season; Stanford (29-5) was Pac-12 regular-season co-champions with Utah before falling in the semifinals of the conference tournament to UCLA.