OAKLAND -- Blake Treinen’s 2019 season has not gone the way he imagined, and it came to an abrupt end on Wednesday afternoon.

Following the A’s 1-0 walk-off victory over the Royals in 11 innings, manager Bob Melvin revealed that Treinen would be shut down for the final nine games of the regular season due to a stress reaction in his back. The injury dates back to a four-game series in Kansas City last month, when Treinen experienced what he thought was just regular soreness until an MRI on Sunday revealed the severity.

“It was similar to issues I had in the past that would kind of just go away,” Treinen said. “I tried to figure it out and get through it, but it wasn’t getting better. I think we’re just going to try to keep things calm these next couple of weeks.”

After establishing himself as one of baseball’s elite closers with a historically dominant 2018 season, Treinen struggled to close games in the first couple of months of 2019. The 31-year-old lost the closer’s role to Liam Hendriks in June, and though he showed flashes of his old self at times over the past few weeks with scoreless outings in eight of his last 11 appearances, the right-hander entered Wednesday with a 4.91 ERA in 58 2/3 innings.

Treinen’s regular season is over, but he remains hopeful that the rest over the final stretch will help him return should the A’s make the playoffs. After Wednesday’s win, Oakland remained in control of the top American League Wild Card spot.

“It’s not fun to just sit back and not be on the field. But there are other ways to be a good teammate and support these guys,” Treinen said. “It sucks to see guys out there grinding every day and not being able to help with some innings. That’s probably the hardest part.”

Jesus Luzardo and A.J. Puk, Oakland’s No. 1 and 2 prospects respectively per MLB Pipeline, have already been contributing in critical late-inning bullpen roles this September, and Melvin’s dependence on those electric left-handers will only increase in Treinen’s absence.

Chris Bassitt, who has built up a 10-5 record with a 3.95 ERA in 25 starts this year, will also move to a relief role for the remainder of the season in order to provide length.

“We had six guys in our rotation, so with the way guys are pitching, we need some more depth in the bullpen and Bassitt is willing to do it,” Melvin said. “He’s going to do whatever it takes to help the team. He’s a competitor and he’s done both in the past. That’s the one thing about Chris. He’s really versatile.”