Washington, DC (SportsNetwork.com) - An already rough road trip just got even worse for the New York Yankees, as leadoff hitter Jacoby Ellsbury injured his right knee during Tuesday's loss to the Washington Nationals and was placed on the 15-day disabled list following the game.

Ellsbury appeared to hurt his knee during an at-bat in the fourth inning. He ended up drawing a walk and moved to second on a groundout, but Yankees manager Joe Girardi and assistant trainer Mark Littlefield came out to check on the veteran center fielder after witnessing him favor his right leg as he reached the base.

The four-time American League stolen base champion remained in the game and eventually scored on a single from Chris Young, then was replaced in the field during the bottom of the inning.

Ellsbury had been a key to New York's early-season success, as his .324 average and 29 runs scored lead the team and the 31-year-old entered Tuesday's game tied for second in the majors with 14 stolen bases.

The Yankees will select the contract of outfielder Slade Heathcott from Triple-A Scranton/Wilkes Barre to fill the available roster spot.

Heathcott, New York's first-round pick in the 2009 MLB Draft, is hitting .285 with one home run and 17 RBI in 37 games for the RailRiders this season.