CHICAGO -- Cubs outfielder Jason Heyward left Sunday's game against the St. Louis Cardinals due to light-headedness and shortness of breath, according to manager David Ross. The team sent him to the hospital for further tests.

"He said he felt a little light-headed after his first at-bat," Ross said following the Cubs' 7-3 loss. "He's not a guy you ever have concerns about, so when he says he's having trouble breathing and is light-headed, you want to make sure everything is all right."

Ross wasn't certain what doctors were testing for and didn't have a timetable for Heyward's return. He went 0-for-2 with a strikeout before being removed from the game.

Heyward has been one of the better hitters on the Cubs this season while playing solid in right field.

"None of us know to what extent or how serious, but he's a big loss, not only with how well he's playing but also [being] a leader in the dugout," teammate Jason Kipnis said. "We're all concerned."