"Harper tried to beat out an infield grounder in the first, when he hit the bag at first [base] awkwardly. As his left foot made contact with the bag, it slipped over the top, and his leg appeared to buckle as he fell to the ground past the base, grabbing his leg by the knee," Collier noted.

Todd Dybas of the Washington Times relayed a screenshot of Harper not being able to put any weight on his injured leg:

Todd Dybas @Todd_Dybas

This is terrible looking.

"We just ask for prayers that it's not serious," manager Dusty Baker said, per Collier. "We're just urging everybody out there that are Nationals fans and baseball fans to say a prayer for him tonight, because he was in obvious pain out there. We're just hoping for the best."

Any significant injury to Harper could be devastating to the Nationals lineup, even with plenty of other talented players on the roster. With Adam Eaton already out for the year with a torn ACL, the World Series contenders are getting thin in the outfield.

In reality, losing a player of Harper's ability would be damaging for any team.

The 24-year-old is as fearsome a hitter as anyone in the sport, reaching the All-Star Game in four of his first five seasons.

He took home the 2015 National League Most Valuable Player award after leading the league in home runs, runs and on-base plus slugging. He batted .330 that season with a career-best 42 home runs.

After a down year by his standards in 2016, he is once again among the league's top hitters in 2017, batting .326 with 29 home runs and 87 RBI.

This latest injury could put a damper on the impressive season and create trouble for the Nationals. Adam Lind could be the first replacement option after his strong start to the year, although the entire roster will have to contribute to keep the offense afloat as long as Harper is unavailable.