ATLANTA >> Mike Trout will not be returning to the Angels lineup when he’s eligible to come off the injured list Monday.

Head athletic trainer Mike Frostad said Saturday that Trout had a cortisone injection in his back Thursday, so for now his activity is limited.

When asked how much more time Trout might need, Frostad said the Angels don’t know.

“We just have to take it day by day on how he’s feeling,” Frostad said. “There’s a little down period after you get a cortisone injection. We’re just going to let that take effect, and then we’ll keep evaluating after that.”

Frostad said right now Trout can’t do any activities that involve rotation.

Frostad also clarified how an injury that was initially described as back spasms could become left rib cage inflammation. He said they are just different elements of the same injury.

“It all kind of goes together,” Frostad said. “The spasms occur because you’ve got the irritation in the back, in the rib cage. The muscles over top of that are trying to protect it. And that’s what caused those spasms. It all goes hand in hand.”

Trout said last week that he had begun feeling an issue in his back at the start of the month, and it became serious enough for him to come out of the game July 12. The Angels said he was day-to-day for a few days, and Trout actually was back in the lineup last Saturday. But he was scratched just minutes before the first pitch, and a couple days later the Angels placed him on the 10-day injured list.

Trout said at the All-Star Game earlier this week that he still doesn’t feel this is anything like last year’s calf injury, which ended up being much more serious than the initial expectation.

While Trout is out, Brandon Marsh will be the Angels’ center fielder.

Manager Phil Nevin said when Trout was only out for a few days, he wanted to keep Marsh in left, where he’s played well, but now that this is a “little bit more of an extended time with Mike,” he is putting Marsh in center because he’s the best outfielder.

More medical news

Right-hander Michael Lorenzen (shoulder strain) had been scheduled to pitch at Double-A this week, but the Angels scratched that and have stopped his throwing program.

“He just wasn’t quite at the point where throwing off a mound was beneficial for him,” Frostad said. “He’s going to begin throwing again within the next couple of days. He just needed a little bit more time.”

Right-hander Jimmy Herget (shoulder impingement) was scheduled to pitch at Double-A on Saturday. Frostad said Herget is expected to pitch two more times in the minors, although it could be more or less depending on how he does.

Infielder Matt Duffy (low back spasms) has been working out in Arizona, including some baseball activities. “We’re hoping to get him back sooner than later, get him out on a rehab,” Frostad said.

Infielder David Fletcher (hip surgery) is still playing at Triple-A. “He says every day is an improvement from the day before,” Frostad said. Fletcher had said before the break that the plan was for him to be activated at the start of the Angels’ next homestand, on Thursday.

Right-hander Archie Bradley (broken elbow) will have an X-ray on Monday to determine if he’s ready to begin some baseball activities. He is on the 60-day IL, so he’s not eligible for another month.

Right-hander Griffin Canning (back) is still in limbo, waiting for his back to improve enough for him to increase his activity. Frostad said the Angels are still trying to “exhaust every option before we go into surgery.”

Right-hander Chris Rodriguez (shoulder capsule repair surgery) is throwing in Arizona, but not off a mound.

Pitching plans

The Angels have Noah Syndergaard and José Suarez scheduled for the first two games in Kansas City, but they aren’t sure who will start the series finale Wednesday.

Shohei Ohtani is scheduled to pitch Thursday, the first game of the homestand against the Texas Rangers.

Manager Phil Nevin said he’s considering giving Ohtani a day off sometime in the next week.