Doctors are still trying to determine what caused the medical condition, the celebrity news website said.
Friends took the actor, musician and occasional race-car driver to an Arizona hospital Friday after he had trouble speaking and understanding words, TMZ said.
He was told he suffered a mini-stroke and tests are being conducted to find out why.
Muniz's film credits include "Big Fat Liar," "Stuck on You" and "Agent Cody Banks."
2014: The Year in Music [PHOTOS]