"It was nothing major; very minor stuff," Stewart said. "We wanted to be cautious about it and not push it. Hopefully [Monday] works out and I'm in there."
Stewart was forced to depart Saturday's 11-1 loss to Boston in the fourth inning due to symptoms of dehydration, saying afterward that he had felt light-headed but could have finished the game.
"I've had heat exhaustion where I played in very hot weather, very humid weather, and it wore on my body," Stewart said, "but nothing to where it kind of messed with my head a little bit."
Stewart was replaced behind the plate for Sunday's game by catcher Austin Romine, who went 1-for-1. Stewart is batting .262 with three homers and eight RBIs in 32 games, and manager Joe Girardi said that it would not be prudent to go with just one available catcher on the roster for very long.
"We're a little concerned or we wouldn't have sent him for a test," Girardi said. "We're hoping he comes in [Monday] and feels really good."
If anything happened to Romine, shortstop Jayson Nix would have served as the Yankees' emergency catcher.
Bryan Hoch is a reporter for MLB.com. Follow him on Twitter @bryanhoch and read his MLBlog, Bombers Beat. Josh Vitale is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.