Retired official Urs Meier insisted Anders Frisk's decision to quit refereeing after receiving threats was surprising but understandable.
Frisk, 42, of Sweden, retired with immediate effect on Friday following threats against the life of his family.
He told the Swedish media that the last 16 days had been "the very worst".
"I was surprised but I can understand him. He is afraid," Switzerland's Meier, who had death threats following Euro 2004, told BBC Radio Five Live.
Meier added: "I was a little bit shocked because he is 42-years-old.
"I was 45 and that's why, for me, the career was in the end.
"But he is one of best referees in the world and has the Euros and World Cup in front."
Frisk was in charge of Barcelona's controversial 2-1 Champions League win over Chelsea in February.
He was also hit by an object thrown from the crowd at Roma in September.
Chairman of Sweden's football referees' association, Bo Karlsson, told Sportsweek: "Frisk is feeling danger for his own and his family's life.
"He is saying here in the Swedish press that the last 16 days have been the very worst for him.
Meier was forced into hiding in Switzerland after Euro 2004
"He had not said what was in these messages. He has kept that to himself.
"But most of this is coming from England."
Meier was forced into hiding after receiving death threats following his decision to disallow Sol Campbell's goal for England in the quarter-final against Portugal at Euro 2004.
His personal telephone number and e-mail address were published in some English tabloid newspapers.
Meier said: "For one week after this game there were two policemen with guns protecting my house and office.
"The police say to me I have to go undercover to another place for four or five days so nobody knows where I am.
"I had no possibility to meet my children, for example. The police said it was too dangerous to go home.
"It was the most negative point in my career."