More bad news for baseball ... the Chicago White Sox say they're quarantining their manager, Ricky Renteria, after they say he woke up Monday displaying COVID-19 symptoms.

The team says 58-year-old Renteria had a "slight" cough and nasal congestion ... and immediately went to the hospital for coronavirus testing.

White Sox general manager Rick Hahn says Renteria will quarantine at the team's hotel -- and will NOT manage in Monday's game against Cleveland -- while he awaits testing results.

Of course, MLB is experiencing a surge in COVID-19 cases ... the Marlins had a large outbreak over the weekend that reportedly included 11 players and 2 coaches.

In fact, the worry of COVID spreading through the league is so rampant ... MLB announced it's postponing Monday's Marlins vs. Orioles game as well as the Phillies vs. Yankees game.

The White Sox, meanwhile, say they'll be managed by bench coach Joe McEwing when they play Cleveland at 4:10 PM PT in Ohio.