Ogwumike is opting out for health reasons.
"This year is unprecedented in many ways, therefore my team and I have come to the decision to be proactively cautious and put my body first," Ogwumike said.
As for Toliver, she's electing not to partake due to the risk of injury and the danger associated with playing through the coronavirus pandemic.
"During my time away I will get myself mentally and physically prepared for the 2021 season, and in light of the many social justice issues that are finally and rightfully front and center, I will find new ways to make a positive impact in my community," Toliver said.
The Sparks' other 10 players have all opted into the 2020 season, according to SB Nation's Brady Klopfer.