(Gary Cameron / Reuters)

The Nationals are reviewing the results from an MRI of Danny Espinosa’s left shoulder to determine their next course of action. In the best-case scenario, one team official said, Espinosa would receive a cortisone shot, miss a few games and play through the fall with some pain. In the worst-case scenario, the shoulder injury would require a more serious step, and Espinosa would miss a significant chunk of the remainder of the Nationals’ season, if not all of it.

Espinosa had been feeling the pain in his shoulder for roughly a week, and he played through it until late Sunday night, when he told hitting coach Rick Eckstein he no longer could. In the ninth inning, Manager Davey Johnson pinch-hit for him with Steve Lombardozzi, the Nationals’ backup second baseman.

“He was hurting,” Johnson said Sunday night.

Espinosa, Johnson said, had discussed his injury with Adam LaRoche to see if it was similar to what LaRoche endured last season. LaRoche underwent surgery to repair a torn labrum in his left shoulder, which led to him missing the final 123 games of 2011.  

Losing Espinosa for any significant amount of time would be a blow to the Nationals’ chances in the postseason, even if they do have a viable, tested backup in Lombardozzi. The switch-hitting Espinosa is batting .250/.315/.407 this year with 16 homers. He rebounded from a rocky first half to become a far more dangerous hitter, hitting .272/.323/.449 with nine homers since the all-star break.

Espinosa has struck out 174 times, which leads the National League, and he has endured some major valleys. But if you fixate on his strikeout totals or what he does at his worst, you miss the point.

Espinosa’s power changes the Nationals’ lineup, giving the Nationals a legitimate extra-bases or home run threat hitting seventh. How many National League teams can say the same? When they’re at full strength, the top seven hitters in the Nats’ lineup are capable of hitting 20 homers in a season. How many AMERICAN League teams can say that? They’d lose some of that depth without Espinosa.

Espinosa’s defense makes the Nationals different, too. He has outstanding range and one of the best infield arms in the majors. On cuts and relays, the threat of his arm can stop runners from trying to score and turns triples into doubles. He has played in 144 of 146 games and, before now, was the only Nationals regular to experience no apparent injury concerns all season.

FanGraphs.com’s formula gives Espinosa credit for 3.7 wins above replacement, tied with Brandon Phillips for the National League lead among second basemen. The WAR stat shouldn’t be taken as definitive, but it is a strong sign that Espinosa has been one of the best at his position this year.

In Lombardozzi, the Nationals have a potential substitute for Espinosa who can give them more than replacement-level production. Lombardozzi has already started 80 games this year, toggling around the infield and to left field – a position he learned late in spring training – to fill in for any regular forced out with an injury.

Lombardozzi cannot match Espinosa’s power at the plate or athleticism in the field. But he finds other ways to contribute. He has reached base at a .323 clip this year, and he plays steady defense – he has made three errors all season, only one of them at second base in 219 chances. If he can get to the ball, he’ll field it cleanly and make an accurate throw.

“I don’t ever have to watch him, because he’s always in the right spot,” Nationals bench coach Randy Knorr said earlier this year. “You look, and he’s standing there. Just throw him out there, he’ll figure it out.”

The Nationals would still be a complete team with Lombardozzi starting at second base. But they have a lower ceiling if Espinosa is not available. He is one of their best players, and facing the postseason without him would deliver a major hit.

But the Nationals have absorbed those kind of blows all year and managed to win under every circumstance. It would be hard for them to win without one of their regular players, but after playing — and thriving — during portions of the season without Ryan Zimmerman, Michael Morse, Jayson Werth, Wilson Ramos, Ian Desmond, Drew Storen and others, it would be nothing new.