MILWAUKEE -- The Pirates’ starting rotation has remained remarkably healthy this season.
That changed Monday, as they announced Mitch Keller will be out for the season with a teres major muscle injury in his right shoulder.
Keller won’t throw for six to eight weeks, preventing a possible return. The teres major is one of the muscles controlling the shoulder joint, extending from the shoulder blade to the top of the arm. It's partially responsible for extending the arm, which obviously causes problems for a pitcher.
"We had a decent idea with Mitch [Sunday] postgame after he came out, a little bit of information," Pirates general manager Ben Cherington said, describing Sunday's loss in Cincinnati.
"Got more information [Monday] once we had the MRI. Now, just got to work with Mitch to get past this and get healthy and get into a really good offseason, which we're confident he'll do."
Cherington explained that he doesn't think the injury hampered Keller, who has a 5.29 ERA in 22 starts. It was likely something that happened at Great American Ball Park.
"He wasn't reporting anything," Cherington said. "He did report it after coming out of the game [Sunday]. So, it was certainly the first that I'd heard about it.
"He's a tough guy. He wants to be out there and he obviously wasn't himself yesterday and there's a reason why. We have that now."
Sunday’s series finale in Cincinnati was especially bad for Keller, who recorded just six outs and allowed seven earned runs, struggling with his command while walking four and giving up two long homers.
The start was frustrating for Keller because it also came after he put together two starts where he allowed two earned runs over 10 1/3 innings to seemingly start to get his season back on track.
Instead, the Pirates will need to fill his rotation spot.
Asked Monday whether that means Carmen Mlodzinski will go back to starting, Cherington deferred those questions to manager Don Kelly.
Cherington did say that Keller's injury was an input when it comes to the addition of Lake Bachar from the Marlins. Bachar has experience working multiple innings and could potentially take over Mlodzinski's old role.
"We just wanted to add as much depth as we possibly could and give us and give Donnie as many options as possible to fill out those innings," Cherington said.
This year actually started well for Keller, who had a 2.85 ERA over his first seven starts. But since that time, he has a 6.63 ERA over his past 15.
Outside of Jared Jones starting the season on the 60-day injured list due to internal brace surgery, Pirates starters had remained on turn.
Following Sunday’s game, Keller talked about what the Pirates need to pull out of their current funk -- they’ve lost 10 of 16 since the All-Star break -- and he accurately cited starting pitching, saying he knows that group can be better.
“We have to anchor the team a little bit better,” Keller said. “It’s just not acceptable for what we’re doing or what we’re capable of doing.”
Pirates starters have a 4.28 ERA in those 16 games (since July 17), which ranks 23rd in MLB. They’re in the same spot when it comes to the group’s WHIP (1.37).
Cherington did not express concern over the severity of the injury or the ability to recover from it. At the same time, "odds are he's not going to pitch in 2026."
"I think the goal now is just helping him get to a spot where he’s having a really good offseason and he’s going into 2027 feeling really good and in a better spot than he has been of late," Cherington said.
Jason Mackey: Jason.Mackey@pirates.com and @JMackey_PGH on X.