"Akeem's condition remains very critical," said the club's managing director Pal Oroszt, while a statement on the club's website described the player's state as "still critical, life threatening".
Adams, 22, suffered the heart attack at his Budapest home late Wednesday after a training session and a team meal, various media reports said.
The player managed however to alert his teammates, who called an ambulance. Since then, he had undergone three emergency operations at a Budapest hospital, Orosz said. The club's rivals Ujpest have come forward to wish Adams a speedy recovery via Twitter.
Adams has eight international caps and represented Trinidad and Tobago at the 2007 Under-17 and 2009 FIFA U-20 World Cups.
He has played six matches for Ferencvaros since joining the team in July.