Swedish referee Anders Frisk will not reverse his decision to retire after he received death threats following Chelsea's European tie in Barcelona. The 42-year-old quit the game after he was heavily criticised by Blues boss Jose Mourinho after the Nou Camp clash.
"I thought about not retiring and then decided and the decision is not reversible," said Frisk.
"What happened after the Chelsea match started currents and dark things which made me feel this cannot go on."
He added: "I have gone through many matches and stood up straight in many strong winds but this was one wind and one match that I wanted to get away from."
Chelsea coach Mourinho accused Frisk of speaking to Barca coach Frank Rijkaard at half-time and Uefa's referees chief Volker Roth called Mourinho the "enemy of football" after Frisk retired.
But Uefa's director of communications William Gaillard absolved Mourinho of any blame for the Swede's decision.
"No-one at Uefa has linked Mourinho's comments with the resignation of Anders Frisk," said Gaillard.
"This is not on the agenda for our next executive committee meeting."
But Mourinho's behaviour and the conduct of Chelsea will come under scrutiny by Uefa's control and disciplinary committee at a hearing on 24 March.