Tom Withers of the Associated Press added that the star won't throw for two weeks as he recovers from the injury.
Bieber, 26, emerged as baseball's best pitcher in 2020, finishing 8-1 with a 1.63 ERA, 0.86 WHIP and 122 strikeouts in 77.1 innings. His ERA and strikeouts all led Major League Baseball, and his wins were tied with Yu Darvish.
Unsurprisingly he was named the AL Cy Young award winner and finished fourth in MVP voting. He was expected to pair with Zach Plesac atop Cleveland's rotation again in 2021, giving them a fantastic one-two punch.
It's worked so far as Cleveland is 34-28, five-and-a-half games behind the Chicago White Sox for first place in the AL Central.
Bieber has made 14 starts with a 3.28 ERA, and he leads MLB in innings pitched (90.2). His 130 strikeouts are also an MLB-best.
Cleveland has chosen to utilize a very young rotation behind them, however, after dealing Mike Clevinger to the San Diego Padres and Carlos Carrasco to the New York Mets in the Francisco Lindor trade.
Yes, Cleveland received quite a prospect haul for those established players. But it was a punch to the gut for fans of the organization, who were eager to see the team finally end its title drought.
Bieber's injury, if more serious than it already is, will be the next gut-punch. The team called up Kyle Nelson from its Triple-A affiliate to fill the void.