As a result of the positive tests, the Cardinals' four-game series against the Detroit Tigers, set for Tuesday to Thursday, has been postponed. The Cardinals have been in quarantine since last Thursday and will stay in Milwaukee, and their personnel will continue to be tested daily, MLB said.

The outbreak among Cardinals' players and staff raises further questions about MLB's plans to safely hold the season amid the coronavirus pandemic. Last week, 21 players and staff on the Miami Marlins tested positive for coronavirus, and the Philadelphia Phillies have also had several positive tests.

Commissioner Rob Manfred warned union leader Tony Clark in a Friday call that if the league and players don't do a better job of following Covid-19 protocols and managing the virus, Manfred could shut down the shortened season, ESPN reported.

MLB is tentatively planning for the Cardinals to resume their season August 7 against the Chicago Cubs.

The league's extensive protocols for holding the season included banning high-fives and spitting by players and keeping fans out of stadiums. But teams are still traveling the country to play games in empty stadiums and are not isolated from the general American public.

In contrast, the NHL, NBA and WNBA have restarted their leagues without positive tests by holding all games in "bubbles," where players are consistently tested, are required to masks and remain apart from the public.

Manfred has said that holding the baseball season in a "bubble" would not have worked because MLB has large teams and wants to hold a 60-game season.

"The duration would have been much longer, and the longer you go, the more people you have, the less likely it is that you can make the bubble work," he said.