Cincinnati did not disclose why Votto was placed on the IL. However, the veteran infielder apparently self-reported symptoms related to COVID-19, a source told Bobby Nightengale of the Cincinnati Enquirer.
Votto has not tested positive for COVID-19, Nightengale adds.
It's the second weekend in a row the Reds have put a star player on the IL for an undisclosed reason.
Mike Moustakas was placed on the IL last week after he said he wasn't feeling well.
Because of COVID-19 concerns, Moustakas and teammate Nick Senzel missed three games due to league-mandated absences after they self-reported symptoms.
The pair eventually appealed the decision after testing negative on multiple occasions. They returned to the Reds' lineup July 29 after winning their appeal.
With Votto injured, Cincinnati reinstated right-hander Anthony DeSclafani from the 10-day IL to take his spot on the roster.