Keller tested positive for COVID-19 on Tuesday, Andersen Pickard of MLBDailyDish.com reports.
Keller said that he's experienced only mild symptoms, Alec Lewis of The Athletic reports, but he'll have to go into isolation and won't be allowed to return to the field until he tests negative twice. He's expected to be one of the Royals' top starters this year, but his positive test likely means he won't have enough time to get into game shape by Opening Day.