(Nick Wass/AP)

The Nationals feel comfortable with LaRoche as their first baseman, but Johnson also wants a right-handed backup who could platoon with LaRoche and give him rest. That’s Johnson considered the temporary loss of Chris Marrero a significant setback.

Marrero tore his hamstring playing winter ball in the Dominican Republic and will likely return by the all-star break, Johnson said. Johnson had planned to use Marrero, who played everyday for the final month of last season, as his security blanket for LaRoche.

“Marrero was a guy that could give us insurance with LaRoche,” Johnson said. “His injury kind of left us another man short, as far as I’m concerned. “That right-handed bench player, utility player, is very important. I feel 100 percent sure Adam LaRoche is going to be fine. But it would be nice to have a guy who could step in over there like Marrero did last year.”

In trying to replace Marrero for the first half of the season, the Nationals have considered 36-year-old free agent utility man Mark DeRosa. Johnson managed DeRosa in the 2009 World Baseball Classic, and last week he called him to talk about playing for the Nationals.

DeRosa suffered through two lean, injury-riddled seasons with the San Francisco Giants the past two years, hitting .235/.313/.279 over just 73 games. In his 14-year career, DeRosa has played every position except pitcher, catcher and center field, including 33 games at first base.

“He’s a really quality guy,” Johnson said. “I really like him. If he’s healthy, he fits the role about as good as you can get. He can play just about anywhere.”