The Royals’ already thin rotation, which was missing right-handers Brad Keller and Jakob Junis due to COVID-19, just got even thinner Tuesday.

Kansas City placed left-handers Foster Griffin (forearm strain) and Mike Montgomery (lat strain) on the injured list, and recalled outfielder Nick Heath and right-hander Jake Newberry, who had been on the taxi squad.

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Both Griffin and Montgomery pitched in Monday’s 14-6 win over the Tigers. Griffin, making his MLB debut, got the victory. Montgomery started and gave up five hits and five runs, three earned, over two innings.

But Griffin came out of the game in the middle of the fourth inning, grabbing his left forearm in obvious discomfort.

Manager Mike Matheny had expressed concern earlier Tuesday about Griffin’s injury. It is expected that Griffin will return to Kansas City to get an MRI.

“We kind of anticipated [injured list] to be the case,” Matheny said.

Montgomery’s injury had not been previously revealed.

“He wasn’t right,” Matheny said. “It was something we had to get on top of.”

“It’s something I started feeling back in the Houston [exhibition game] last week,” Montgomery said in a Zoom call. “I thought it was really just normal soreness. We have been used to 6-8 Spring Training weeks to get ready, and now we were doing it in three, so there isn’t a lot of recovery time.

“But it just didn’t feel right [Monday night]. So after talking to Mike and [trainer Nick Kenney], we just felt the best move going forward was to shut it down now. This will give me the best chance to come back and help the team a few weeks from now.”

Meanwhile, Matheny and his staff will be scrambling for starters. Sunday was a bullpen game, with Ronald Bolanos working the first two innings. Reliever Kyle Zimmer was set to serve as an opener Tuesday night, making his first big league start.

Danny Duffy will pitch Wednesday and rookie Brady Singer on Thursday. After that, it’s anyone’s guess.

“We got the next two [starts] covered,” Matheny said. “Bolanos is going to fit into that mix. We’ll try to get him prepped for that.”