The two teams will instead stage a doubleheader Saturday.
MLB Network's Jon Heyman reported a Cardinals coach tested positive for COVID-19, necessitating the postponement.
St. Louis hasn't played since a 3-0 defeat to the Minnesota Twins on July 29. At this point, getting the team to the full 60-game threshold might be impossible, and hitting even 50 games will be a race against the clock.
According to Heyman, 50-plus is the current target. Ken Rosenthal of The Athletic reported the league hopes the Cardinals can get close to a full 60-game schedule and potentially to 60 games with a doubleheader the day after the season ends.
Heyman corroborated a report from former MLB player Jerry Hairston Jr. that "at least a couple" of players visited a casino prior to the outbreak. General manager John Mozeliak and veteran right-hander Adam Wainwright both refuted the rumor.
The St. Louis Post-Dispatch's Derrick Goold also reported that officials from the Potawatomi Hotel & Casino looked at security footage from July 30 and couldn't find any video showing a member of the Cardinals entering the venue.