"We noticed that he's lost some weight over the last little while," Toronto coach Randy Carlyle told reporters Friday after the team skated at the club's suburban practice facility.
Grabovski and the Leafs played in New York on Wednesday and Carlyle said the decision was made to keep him there because of the quality of medical resources there.
Grabovski, whose ice time has been declining in recent outings, only saw 11 minutes of action against the Rangers.
Carlyle says Grabovski has had an ongoing ailment for some two years, with extended periods of heartburn and other discomfort.
"Now it's gotten to a point where he's lost some weight with it and we just felt it was best that we had the best people in the world take a look at him and he was 100 per cent on side with that," said the coach.
Asked if the health issues were behind Grabovski's recent play, Carlyle said: "That's what we're trying to determine."
The 29-year-old Belarusian has eight goals and seven assists in 40 games. Having signed a $27.5-million, five-year contract extension in April, he is the team's second-highest paid player behind captain Dion Phaneuf.
The Leafs, meanwhile, confirmed that star winger Joffrey Lupul has been suffering from a concussion.
Lupul has been out since April 4 when he was sandwiched by the boards between Adam Hall and Jay Rosehill in a 5-3 loss to Philadelphia.
"He skated today, he's improving," Carlyle said. "It's been a day-to-day process with him and he's close."
Carlyle said Lupul didn't exhibit concussion-type symptoms immediately after the incident.
"But that seemed to develop after the first two days," said Carlyle. "As you noticed, he was back on the ice right away.
The winger lost some peripheral vision but that cleared up.
"We thought we were clear of it and then the concussion-type symptoms returned. I guess you could say he had a concussion," the coach added.
Lupul has not been cleared for contact yet, and did not take part in all of the team's practice Friday.
"Right now we're doing the smart thing and making sure that we get it 100 per cent and I'm back playing at the top of my game for playoffs, " said Lupul, who missed more than 20 games earlier this season with a broken forearm.
Toronto (22-13-5) hosts Montreal (26-9-5) on Saturday night.