(Al Behrman/AP)

“They’re going to be pretty tough,” Johnson said.

Mattheus, who will perform fielding drills tomorrow as another test, will soon join Brad Lidge in coming off the disabled list and needing a spot in the bullpen. The Nationals will likely move to a 13-man pitching staff with eight relievers in order to make room, Johnson said.

The Nationals’ bullpen currently consists of Sean Burnett, Tom Gorzelanny, Michael Gonzalez, Ross Detwiler, Tyler Clippard and Henry Rodriguez. Lidge will make his second minor league rehab outing tonight at Class A Potomac and expects to return Sunday in Boston or Monday in Toronto.

As the Nationals begin interleague play in American League parks, they will be less reliant on pinch hitters because of the designated hitter. Johnson implied the Nationals will make room for an eighth reliever by sending third catcher Carlos Maldonado to the disabled list with a back injury.

Even with eight relievers, the Nationals will still need to remove one from their roster once Lidge and Mattheus return – and that’s not considering Drew Storen, who is about a month away from making his season debut.

Mattheus could be the odd man out for now through no fault of his own. Johnson views him as one of the Nationals’ best relievers, but he has a minor league option remaining. Stammen does as well, but he has been invaluable as both a set-up man and a long reliever.

As ever, these things have a way of working themselves out. An injury to a starter – which would move Detwiler back to the rotation – or a reliever would solve the problem for Johnson.

In regard to Mattheus’ health, Johnson said there is “still a little puffiness” in Mattheus’s left foot but, “his arm is in great shape.”

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