Max Scherzer is on the injured list with a mid-back strain, according to the Nationals. (Eric Espada/Getty Images)

PHILADELPHIA — About 20 hours after he said he felt good enough to start soon, Washington Nationals ace Max Scherzer landed on the 10-day injured list with a mid-back strain, the team announced Saturday. The move is retroactive to July 10.

In the corresponding move, the Nationals added catcher Spencer Kieboom from Class AA Harrisburg. It is the first time the Nationals, who also have Yan Gomes and Kurt Suzuki on their roster, have had three catchers this season.

The Nationals could not make the move retroactive to July 6, Scherzer’s last start, because injured list rules stipulate teams can backdate only up to three days. The all-star break did not affect the timing.

After Friday night’s 4-0 win over the Philadelphia Phillies, Scherzer expressed confidence that he and the team’s medical staff knew exactly what the injury was and how to treat it. He also was optimistic that he would start Tuesday in Baltimore for the series opener against the Orioles.

"This is not something to be overly concerned about,” he said at the time. “I know the feeling of what it’s going to take to get back on the mound and get completely through the ball. Like I said, we’re only a matter of days. This isn’t a long-term injury.”

When Nationals Manager Dave Martinez spoke with reporters before Saturday’s game, he had not touched base with Scherzer.

“When he works out, you just leave him alone,” Martinez said with a laugh. “As soon as he’s done, I’ll talk to him.”

Earlier that afternoon, Scherzer had played catch briefly before heading back into the dugout. But an hour after reporters left the manager’s office, the Nationals announced the move. Scherzer cannot return until July 20, the third of a four-game series in Atlanta against the Braves. Now Washington’s rotation faces a challenge to get there. Without Scherzer, the Nationals will need at least one spot starter for Tuesday.

The Nationals might need another for Wednesday, as well. The team’s No. 2 starter, Stephen Strasburg, could go that day on regular rest if the Nationals use Monday’s off day as a chance to implement a four-man rotation for the first week-and-a-half back from the all-star break. Asked whether the four-man approach was a possibility before Saturday’s game, Martinez said the team was leaving its options open. It’s unclear how the Scherzer news impacts that plan.

For spot starters, the Nationals probably have three options, including Joe Ross from Class AAA Fresno or Austin Voth from Class AA Harrisburg, who could both start Tuesday on regular rest. The Nationals also could call up Erick Fedde from Harrisburg. The right-hander has not pitched since July 2 because of overlapping all-star breaks during his transfer from Fresno to Harrisburg.

Scherzer had been dealing with back tightness since July 1, the day after his start in Detroit against the Tigers. The injury, Scherzer said, is the result of his back supporting his shoulder blade when he pitches. Scherzer later received treatment, and his body felt well enough to start five days later against the Kansas City Royals in his final start before the all-star break. He struck out 11 in the 6-0 win. After the game, though, Scherzer felt his back tighten again, and following a conference with Nationals General Manager Mike Rizzo and Martinez, he decided to withdraw from the All-Star Game.

In Cleveland for the All-Star Game, Scherzer tried to play catch Tuesday but could not. The next day, he got an MRI exam, which came back clean. Scherzer interpreted the result as a muscular issue and nothing more. Still, he had calculated the number of days until his next scheduled start and the days of rest he needed between his next bullpen session and realized “it just wasn’t going to happen.”

In his past nine starts, Scherzer has a 0.84 ERA with 94 strikeouts and just nine walks in 64 innings. He is accustomed to being one of the most durable pitchers in the game, and he has thrown more than 200 innings in each of the past six seasons. He leads the NL with 129⅓ innings. In June, he pitched seven scoreless innings one day after suffering a broken nose. So on the first day back from the all-star break, Scherzer threw from as far as 75 feet and felt good again. Martinez joked, “You know Max; he always feels like he’s ready to go.”

The Nationals still pushed his start back for precautionary reasons. Scherzer reassured everyone — while knocking on the wood of his locker — that everything else in his body felt fine. He pointed out this injury couldn’t have happened at a better time.

“We’ve been kind of lucky to have the all-star break to get the rest that I need,” Scherzer said Friday. “We know exactly what this is. It’s just a matter of getting this right and making sure it doesn’t linger any further in the season.”

Despite the Scherzer news, the Nationals were fortunate Saturday in regard to their upcoming series in Baltimore.

The Orioles, the worst team in baseball with a 28-63 record entering Saturday night, are flailing more than usual. None of their three best starters will pitch against the Nationals. On Saturday, Baltimore placed Dylan Bundy on the 10-day IL with a knee injury and traded Andrew Cashner to the Boston Red Sox. All-star left-hander John Means pitched for the Orioles on Saturday.

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