Gail Burton/Associated Press

Davey Johnson had liked Denard Span for three or four years, but that’s not even the first reason he thought General Manager Mike Rizzo pulled off a great deal today when he traded for him. Johnson believes Span’s addition gives the Nationals the left-handed bat their lineup needed in the event first baseman Adam LaRoche does not re-sign.

“I think it was a great trade,” Johnson said. “I think this is a hell of a move, because it gives us some protection if Adam leaves. I’ll still have some left-handed presence in the lineup.”

Johnson did not want to venture how he would align his lineup behind the leadoff-hitting Span, because it would depend on whether LaRoche returns or Michael Morse plays first base. If LaRoche leaves, it may make the most sense for Harper to hit cleanup to protect Ryan Zimmerman with a left-handed bat.

In the outfield, Johnson will have to choose who plays on which corner between Jayson Werth and Harper. Johnson said it’s not much of an issue, and he’ll essentially leave it up to the players.

“I would probably check with my resident genius Werth and see what his preference is,” Johnson said. “I’m comfortable with him there. The young stud could play either one.”

Johnson has not given up on signing LaRoche, whom Rizzo said the Nationals are still discussing a contract with. Johnson texted LaRoche today about attending his charity golf tournament over the weekend. “Bring your pen,” Johnson wrote – meaning to sign a contract.