PFA chief executive Gordon Taylor fears for the future of Luis Suarez's career following an alleged bite of an opponent.
The Liverpool forward faces a possible two-year or 24-match ban from FIFA if found guilty of biting Italy's Giorgio Chiellini during Tuesday's group game.
"It is a big problem for Liverpool," said Taylor. "I fear for his career."
Suarez has twice before been charged in biting related incidents, his first offence whilst playing for Ajax in 2010. After biting Chelsea's Bransilav Ivanovic during a Premier League match in March 2013, Suarez was given a 10 match ban.
Returning from suspension he won the PFA and Football Writer's Player of the Year Award and scored 31 goals last season as Liverpool finished as runners up in the Premier League.
"He seemed to get back on track. He had a great season,"
"There are mental health issues and he certainly needs to eradicate this from his make up."
FIFA opened disciplinary proceedings against Suarez after referee Marco Rodriguez took no action following the 80th-minute incident. Suarez and the Uruguayan Football Association have until 21:00 BST on Wednesday to respond.