The fourth official at the Champions League game between Barcelona and Chelsea at the Nou Camp has accused Jose Mourinho of lying.
The Blues boss said he saw referee Anders Frisk speaking to Barca coach Frank Rijkaard at half-time.
But Martin Ingvarsson said: "What Chelsea are saying is a lie. There was no chat between Frisk and Rijkaard."
Frisk later quit after receiving death threats and Mourinho was branded an "enemy of football" by a Uefa official.
Uefa referees' committee chairman Volker Roth said: "We can't accept that one of our best referees has been forced to quit because of this. People like Mourinho are the enemy of football."
The Chelsea boss hit back by threatening to sue Roth unless he received an apology.
"Mr Roth has two ways out, apologise or it goes to court," he said.
"I feel like a hunted animal and I don't want a life like that"
And on Tuesday, Roth responded: "I have heard that Mourinho is threatening to sue and I am looking forward to seeing what his complaint is."
Chelsea lost the first leg 2-1 and had Didier Drogba sent off in the second-half.
Mourinho was highly critical of Frisk's performance, and claimed he saw Rijkaard entering the Swede's dressing-room.
But fourth official Ingvarsson said: "No one came into our dressing room and I don't know why they are saying it. I saw what happened.
"It is very sad that Anders has retired over this, he had done nothing wrong and had a good game."
Roth tried to persuade Frisk to go back on his decision, but the Swede would not be swayed.
"I spoke to Volker Roth, but I'm finished. I'm relieved and my gut feeling tells me it's right," he said.
"I feel like a hunted animal and I don't want a life like that. You never know what these people might do.
"Coaches and managers should pause to think what they might start by saying something off the cuff."
Mourinho added: "It's a shame that Frisk has decided to leave football.
"If this decision is linked to the criticism of his performance in the Barcelona game, it seems strange to me.
"There's similar criticism every day, all around the world, for managers, directors and players. It's a normal situation.
"If there are other motives I do not know them and would like them to be known."
Chelsea have said they will act if it can be proven that their own supporters made the threats that convinced Frisk to retire.
A club statement said: "The club and our manager condemn any threats made to Mr Frisk, his family or friends.
"If there is any evidence of such behaviour by Chelsea fans then we would totally disassociate ourselves from them.
"We would welcome any such evidence to be passed to us so we can investigate and take the appropriate action."