Not only did the Yankees lose on a walk-off home run last night to the Nationals, but they've also lost Jacoby Ellsbury for at least a stretch of time.

The outfielder was placed on the 15-day disabled list after hurting his knee, apparently on a swing in the fourth inning.

Ellsbury is hitting .324 with a .412 on-base percentage this season. His potential ability to hit for power (32 HR in 2011) and his ability to steal bases (14 steals this year) make him one of the Yankees' biggest offensive threats.

Furthermore, he and Brett Gardner have formed a very formidable top of the order that has helped set the table for the Yanks' lineup.

Ellsbury has missed several games in his career due to injury. He played in just 18 games in 2010 and 74 in 2012.

The Yanks will call up Slade Heathcott to take Ellsbury's place. He is hitting .285 with 17 RBIs at Scranton/Wilkes-Barre.