Reyes will have tests on Monday and it could take up to 48 hours for doctors to receive the results. Reyes is not expected to take part in any physical activity while he is gone.
"We're going to be conservative," Mets general manager Omar Minaya said.
The thyroid is a gland in the neck that produces hormones that help control metabolism.
Doctors cleared Reyes to play Friday after he took a follow-up blood test to one conducted during his physical. However, Minaya said team doctors in New York wanted to take a closer look at the speedy infielder and pulled him out of pregame stretching.
"I know he wants to play bad, but he's going to play enough," manager Jerry Manuel said after the Mets' 4-3 loss to the Florida Marlins. "There's no doubt in my mind that he's going to play. I know he's anxious to get out there."
Reyes appeared in only 36 games last season because of a hamstring injury, which Reyes said has healed. The Mets have discussed moving him from the leadoff spot to third in the lineup while outfielder Carlos Beltran recovers from offseason knee surgery.
Reyes said he felt fine and has not experienced any dizziness, fatigue or any other symptoms of a thyroid problem. He said he was anxious to find out what is happening.
"We're not talking about my leg, nothing like that, we're talking about my health," he said, "so I have to be concerned about it."
Reyes said this is the first time an imbalance was found in a blood test, and maintained that he does not feel "haunted" by injuries after being summoned to New York.
"I don't want to say unlucky because leg-wise everything feels good," he said. "But this is different. We're not talking about an injury on the field."