PHILADELPHIA -- One day after announcing that they were pushing back Max Scherzer's scheduled Sunday start, the Nationals placed their ace on the 10-day injured list Saturday due to a mid-back strain. The club recalled catcher Spencer Kieboom from Double-A Harrisburg to take Scherzer's place on the active roster.

Scherzer was optimistic following Friday's game that he could take the mound as soon as Tuesday against the Orioles, but that will not be the case. His stint on the injured list is retroactive to July 10, meaning that the earliest he can return would be Saturday in Atlanta.

"I talked to Max and he said he felt the same as yesterday, so we decided to just give him those days. We were able to retro it a few days, so he’s available hopefully [next] weekend," manager Dave Martinez said. "We’re at the point now where we need him. So we came to a decision where the best thing to do is just let it rest."

Scherzer's back first flared up following his June 30 start against the Tigers, but the issue subsided prior to his next outing, Saturday against the Royals. It wasn't until after that start, in which he struck out 11 over seven scoreless innings, that his back tightened up again.

That led to his decision not to participate in Tuesday's MLB All-Star Game, though he still made the trip to Cleveland for the festivities. He was hoping to play catch prior to the All-Star Game to prepare for his originally scheduled Sunday start, but that plan was scrapped when his back did not loosen up as much as he had hoped.

Scherzer underwent an MRI on Wednesday, which came back clean.

"This is not a major thing," Scherzer said Friday. "We know exactly what this is, we know it's muscular. The pause for concern is that we tried to get it going for the Kansas City start, and it just wasn't able to recover from the Kansas City start. Now, you got to go on a little different protocol to make sure I'm 100 percent right before I step on the mound again."

The Nationals have an off-day Monday, which gives them some flexibility for filling Scherzer's spot in the rotation. They then play a brief two-game series against the Orioles, followed by a four-game set in Atlanta against the division-leading Braves to wrap up a nine-game road trip.

Scherzer's trip to the injured list comes during arguably the best stretch of a career that has included three Cy Young Awards. He is 7-0 with a 0.84 ERA over his last nine starts, while striking out 94 batters and walking just nine over 64 innings.