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As Stephen Strasburg recovers from a Grade 1 right lat muscle strain, he will rest until at least Wednesday, Manager Davey Johnson said. Johnson added that if Strasburg feels better, he could throw a bullpen session as soon as the middle of the week.

The Nationals have yet to rule out Strasburg making his next start, but given general guidelines for lat strains that seems to be either unrealistic or risky.

One major league medical official said the Nationals are being “overly optimistic” in not ruling out Strasburg’s next start. The same official, speaking on the condition of anonymity to speak freely about another team’s player, said lat strains typically take three to six weeks from which to  to fully recover.

The medical official had not examined Strasburg personally, and so could only speculate based on typical guidelines for a Grade 1 lat strain, the classification the Nationals have given to Strasburg’s ailment.

Lat strains are common for pitchers, the official said, because of the throwing motion wears the lat muscles, which are crucial in the acceleration of the arm. But the injury requires careful treatment and full rest for two reasons.

First, like a hamstring injury, it can sideline a pitcher for far longer than originally expected if he returns too quickly and aggravates the strain. Second, returning with the muscle still strained enhances the risk Strasburg would overcompensate and risk damaging his shoulder or elbow.

There is one relatively promising aspect to Strasburg’s strain. According to Nationals head athletic trainer Lee Kuntz, Strasburg strained a lat muscle in his lower back, not higher around his shoulder blade.

“That’s actually better,” the medial official said. “It’s more of muscular aspect than a tendinous aspect. But it’s like any muscle injury. I would think making his next start is very, very, very optimistic.

“If he pitches again before he’s got a full-range of motion at full strength, that would really surprise me.”

If the Nationals clear Strasburg to throw a bullpen session on Wednesday, he could feasibly start June 8, the first day the Nationals would need a starting pitcher to prevent any of their starters from pitching on short rest.

The Nationals have several moving parts in their rotation. Ross Detwiler has been participating in baseball activity, but has not been given a timetable for when he could return to the rotation from an oblique strain. Detwiler is on the disabled list retroactive to May 16.

Nate Karns, who lost to the Braves on Sunday after allowing four earned runs in 4 2/3 innings, has replaced Detwiler his past two turns in the rotation. Karns has shown promise in his two major league outings, striking out nine batters and walking three in nine innings. He said he had not been given a plan about his next step.

“Nothing,” Karns said. “They haven’t told me anything.”