The Oakland Athletics were dealt a serious blow in the middle of the postseason race and may be without starting pitcher Sean Manaea for the remainder of the 2018 season. 

According to Jane Lee of MLB.com, Manaea was "shut down indefinitely" after it was discovered he has rotator cuff tendinitis. Oakland hasn't ruled out a 2018 return, but Lee cautioned there is "a chance" he won't pitch again for the rest of the campaign.

The southpaw has been a steady source of production in Oakland's starting rotation this year and has a 3.59 ERA, 1.08 WHIP and 108 strikeouts in 27 starts. The ERA and WHIP totals would both be career-bests, and he just allowed zero earned runs in five innings in a Friday victory over the Minnesota Twins in his most recent start.

While the Athletics still have Mike Fiers, Trevor Cahill and Edwin Jackson, this is another blow to their starting rotation. Julian McWilliams of The Athletic reported on Tuesday Brett Anderson was placed on the 10-day disabled list with a forearm strain.

Don't expect any moves, though, as Ken Rosenthal of The Athletic reported the team is "unlikely to add a starting pitcher" even after the injuries and will instead insert Daniel Mengden and Frankie Montas into the rotation.

Oakland is 2.5 games behind the Houston Astros in the American League West but 4.5 games ahead of the Seattle Mariners in the race for the final wild-card position. It will be tasked with holding off the Mariners for the foreseeable future without one of its key pieces in Manaea.