Reliever Brandon Workman took Sale's place on the 25-man roster.
The 29-year-old Sale has been nothing short of superb for Boston in two seasons. In 2017, he went 17-8 with a 2.90 ERA, 0.97 WHIP and a whopping 308 strikeouts in 214.1 innings. That didn't translate to the postseason, however—he gave up nine earned runs in 9.2 innings across two appearances (one start) as the Red Sox were eliminated in five games by the Houston Astros in an American League Division Series.
It was a disappointing showing in Sale's first playoffs, though he came back with a bang in 2018 and has arguably been even better than last season, going 12-4 with a 1.97 ERA, 0.85 WHIP and 219 strikeouts in 146 innings.
He's also been mostly healthy until this point, though inflammation in his left shoulder cost him some time in early August.
Without Sale, the Red Sox's title ambitions would take a major hit.
While the team has solid options behind him in Rick Porcello, David Price and Eduardo Rodriguez—and one of the best offenses in baseball—Sale is the team's ace and the front-runner for the American League Cy Young Award.