(Jonathan Newton/WASHINGTON POST)

“It’s great,” shortstop Ian Desmond said. “I personally know how hard he’s worked, how passionate he is about the game. I hope he takes full advantage of this opportunity. I think they’re really going to give him a chance to see what he’s going to do. And I think he’s not going to let anybody down.”

Marrero is the Nationals’ choice to replace Ryan Mattheus, the reliever they placed on the 15-day disabled list this evening. On days Marrero does not start, he gives the Nationals another bat off the bench they need. When Marrero is in the lineup, Manager Davey Johnson will play Michael Morse in left field, both in order to give Marrero playing time and to prepare Morse for next season, when Adam LaRoche’s return will move him back to the outfield.

Marrero will complete a five-year tour of the minor leagues packed with ups and downs. Former Nationals General Manager Jim Bowden chose him with the 15th pick of the 2006 draft, and his powerful swing quickly made him the Nationals’ top prospect. He switched positions, from third to first, and before the 2008 season Baseball America ranked him the 28th best prospect in the sport. He broke his leg that season, setting back his development.

Marrero struggled at first base, committing 18 errors at Class AA Harrisburg in 2010. The Nationals still added him to their 40-man roster this winter in order to protect him from the Rule 5 draft, and he arrived at spring training having greatly improved his defense. He made only five errors at Syracuse this season, and his swing remained a weapon. He hit .300/.375/.449 this year with 14 homers.

Mattheus found the silver lining in his trip to the disabled list. Johnson and pitching coach Steve McCatty explained him that they wanted to protect Mattheus, and he had already proved himself this season.

“They way Cat explained it, it’s actually kind of encouraging,” Mattheus said. “They’re looking to the future. Looking at me as part of the future is kind of nice. I think you get more concerned when they just keep running you out there and running you out there.

“Early in my major league career, he kind of showed that he had confidence in me. It was reassuring to hear him say it. Especially when you’re injured, you don’t know what’s going on. He tells you, ‘You’ve got nothing to prove to me.’ It’s nice.”

Mattheus will remain with the Nationals and hopes to return to playing catch after “a couple days off.” He wants to pitch again this season.

“I hope to pitch just so there’s no questions going into next year, know that I’m healthy,” Mattheus said. “That’s the biggest thing for me. That’s my main concern, to know that I’m healthy.”