Cleveland Indians starting pitcher Mike Clevinger underwent surgery Friday on a knee injury he suffered during training this week.

According to Zack Meisel of The Athletic, Clevinger partially tore the medial meniscus in his left knee, which has left him on crutches. Meisel later reported that the right-hander is "expected to return to major league game activity" in 6-8 weeks.

The 29-year-old is set to enter his fifth MLB season, and he is expected to be the ace of Cleveland's staff after the organization traded Corey Kluber to the Texas Rangers during the offseason.

The 6'4", 215-pound Florida native is arguably among the most underrated pitchers in baseball, as he has posted an ERA of 3.11 or better in each of the past three seasons.

Last season, Clevinger went 13-4 with a career-best 2.71 ERA, 1.05 WHIP and 169 strikeouts in 126 innings. If not for back and ankle injuries limiting him to just 21 starts, Clevinger may have been a factor in the American League Cy Young Award race. 

Clevinger's biggest MLB sample size came in 2018 when he set career highs with 32 starts and 200 innings pitched. He went 13-8 that season with a 3.02 ERA, 1.15 WHIP and 207 strikeouts.

If Clevinger is forced to miss the start of the 2020 regular season, it will test the depth of the Indians' starting rotation.

While manager Terry Francona can no longer turn to a reliable veteran like Kluber, he has a ton of starting pitching talent that may be able to weather the storm and help the Indians remain in contention for the AL Central until Clevinger returns.

Shane Bieber will likely take over as the No. 1 in the rotation after winning 15 games, posting a 3.28 ERA and being named an All-Star for the first time last season.

Francona also figures to lean more heavily on veteran Carlos Carrasco. The 32-year-old was limited to just 12 starts and 23 appearances last season after being diagnosed with leukemia, but the 2019 AL Comeback Player of the Year is expected to be back in the rotation in 2020.

Behind them are two second-year MLB starters in Zach Plesac and Aaron Civale. Plesac posted a 3.81 ERA in 21 starts and Civale owned a 2.34 ERA in 10 starts last season, so both have the potential to become fixtures in 2020 and beyond.

Adam Plutko, Jefry Rodriguez and Logan Allen figure to battle for the final rotation spot during spring training, but none of them brings the type of experience and production that Clevinger would.