Michael Morse’s injury this spring could lead to some interesting opening day roster decisions. (Henny Ray Abrams/Associated Press)

Monday morning, Brett Carroll strapped on shin guards and pulled on a chest protector, the foreign equipment with which he would pay the price of surviving spring’s harsh arithmetic. Carroll crouched behind a plate. Two coaches stationed 60 feet away fed baseballs into a pitching machine, the speed cranked up.

Carroll knew the Washington Nationals needed an emergency catcher, and so three weeks earlier he volunteered for a job that favored desperation over experience. Four non-roster invitees like Carroll still had a shot to make the Nationals. Two spots, maybe, remained. If he could catch in a pinch, one could be his. The coaches pelted him with balls in the dirt for two minutes, and he was sore for two days.

Said Carroll: “You’re looking to add valueany way you can.”

With one week remaining before opening day, as the Nationals continue constructing the bottom of their roster, the players competing for the last spots anxiously await resolution. Wednesday, they received both clarity and confusion: Michael Morse will likely start the season on the disabled list and Adam LaRoche will not, but the Nationals called veteran Xavier Nady — whom they signed to a minor league contract 10 days prior — to major league camp.

The developments meant the Nationals have two final bench spots for four players: Carroll, Nady, corner infielder Chad Tracy and left fielder Jason Michaels. When Nady boarded the team bus Wednesday morning in Viera, the three others may have tried not to notice. They surely did.

“Let me tell you one thing about the game of baseball,” Manager Davey Johnson said. “They know their competition. They can count — everyone, whatever situation. Whether you’re talking about the outfield situation, the first base situation, I don’t have to say diddly. They know it better than I do.”

The Nationals will make their decision with the knowledge that Morse, barring a setback, will miss a handful of games at most. After he played catch Wednesday morning, Morse underwent a sonogram that revealed the strain in his right lat muscle had “flattened out and healed,” Johnson said. “That was the best news I had all day.”

Doctors cleared Morse to accelerate his baseball activity, but because he has not played since March 13, he still needs to prepare for the season and will probably not be ready by April 5, opening day. A player who begins the year on the DL can debut April 10 so long as he did not play in a spring training game after March 26.

With LaRoche expected to be ready at first base opening day, the Nationals do not need another left-handed first baseman, which limits Tracy’s chances. Carroll’s athleticism and versatility seems to have won him Johnson’s favor.

The Nationals would then choose between Michaels, who has hit .220 this spring, and Nady for the final spots. Michaels has an out clause, meaning he can leave for another major league team if he doesn’t make the Nationals’ roster. Michaels, a 34-year-old veteran whom the Nationals lockered next to Bryce Harper, said he would be willing to accept an assignment to Class AAA Syracuse.

Nady does not have an out clause. But he is the wild card. Nady went 1 for 3 and made a slick backhand play at first base Wednesday, his first major league action after signing a minor league contract with the Nationals on March 18.

“The type of hitter he was wasn’t fresh on my mind,” Johnson said. “After I saw one round of [batting practice], I knew where he was. And I knew I wanted to see a lot of him with us.”

Last year, before a broken hand ended his season in August, Nady hit .248. He also underwent Tommy John surgery for the second time in 2009. “I’m thankful now to finally have nothing” wrong physically, Nady said. “Hopefully I got all the things out of the way that have bothered me.”

His presence will affect the Nationals’ other non-roster candidates. Carroll had already tried to prove his value in any way he could. Tuesday, he took groundballs at first base during batting practice despite no one telling him to. He had played infield in the minors, and he wanted to the let the Nationals know he could play first if necessary.

As the days tick down, Carroll tries to avoid comparing himself with other candidates and sizing up the roster, a mistake he has made in the past.

“I’m human. I’m not a robot,” Carroll said. “But I know in the past when I’ve tried to play GM, it really takes the fun out of the game. It takes the enjoyment out of wanting to play. I’ve really tried to make a commitment — I can’t control any of that. I’m at peace with making that decision.”

Players are on their own trying to gauge their chances. Coaches and executives do not address players’ individual situations, Michaels said, because “there’s really not that much they can tell you.”

The pressure to impress coaches can become a distraction, but only if a player lets it. “I block it out,” Michaels said. “It’s easy to think about it, but it’s out of my control. I just need to stay within myself and play.”

Wednesday, Michaels started in left field and made four outs at the plate. He has bonded with other veterans, becoming a valued voice in the clubhouse. After he walked out of the Nationals’ clubhouse, he paused in the parking lot, next to an idling bus, and considered his current situation.

“It’s a good team,” Michaels said. “I hope to make it.”