A crisis at Portuguese giants Sporting Lisbon that recently saw masked thugs physically attack players and coaches took a new twist on Friday after goalkeeper Rui Patricio stormed out of the club.

Patricio, a target for newly promoted Premier League club Wolverhampton Wanderers, sent a letter to Sporting informing them he was "terminating my contract because of a justified motive".

Portuguese media reports claim the 30-year-old 'keeper, a European champion in 2016 and a member of Portugal's World Cup squad, was motivated by problems negotiating his departure from Sporting.

But in a press conference Sporting president Bruno de Carvalho hit back, pointing the finger of blame at Patricio's powerful agent, Jorge Mendes, whom he accused of greed and of using "blackmail".

"Of the 18 million euros that were on the table, Jorge Mendes wanted seven million," said De Carvalho, adding that Patricio had been "manipulated" by Mendes, who is an advisor to Wolverhampton's Chinese owners.

Patricio retorted, accusing Sporting of "gross negligence" in relation to the attack that shook the club two weeks ago.

"The situation was so out of control that I thought I wasn't going to get out alive," said Patricio.

"I can't even think about returning to that place."

Last month several of the first team players were physically attacked by disgruntled fans wearing balaclavas after they had invaded the club's training complex at Alcochete outside Lisbon.

The supporters broke into the training complex, vandalised the dressing rooms, threatened backroom staff and assaulted players and coaching staff.

In total 23 fans were arrested and face charges relating to the incident.