Chris Sale has tested positive for COVID-19 and will miss his next start.
A Red Sox spokesman confirmed the result on Friday morning, two days before the seven-time All-Star was to face the White Sox in Chicago.
The result is yet another setback for the 32-year-old left-hander, who missed all of last season recovering from Tommy John surgery. Since returning Aug. 14, Sale is 3-0 with a 2.52 ERA.
It's also a setback for the Red Sox, who entered Friday with a one-game lead over the New York Yankees for the AL's top wild-card berth. Toronto was another half-game back as it tries to swipe the second wild-card spot from its AL East rivals.