(Evan Vucci/AP)

Storen threw 32 pitches, but the Nationals want him to prepare more before returning to the majors from surgery to remove a bone chip in his right elbow. Storen, who saved 43 games last year, has yet to pitch for the Nationals this season.

“The consensus among the coaches is his arm strength is not quite where it needs to be,” Manager Davey Johnson said. “I think Drew is champing at the bit. But our concern is that he’s ready, and that he doesn’t have to extra-stress his arm when he gets up here. This is about making sure his arm is ready.”

After four appearances with Potomac, Johnson said, Storen will make his next outing with Class AA Harrisburg. The Nationals will assess Storen after that outing to determine if he’s ready or if he still needs to build more strength in his right arm.

“That’s normal at this stage,” Johnson said. “His arm is just not quite there.”

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