Senior Liberal Democrat officials are to consider a complaint by leadership contender Nick Clegg over a document describing him as a "calamity".
That paper was issued from the camp of leadership rival Chris Huhne.
Writing on his website, Mr Huhne "sincerely apologised" and "disassociated himself from it".
Mr Clegg's campaign team lodged an official complaint with the party's chief whip and party officials are to decide whether to take further action.
Mr Huhne, the party's environment spokesman, told BBC One's Politics Show he had no knowledge of the document.
But, in heated exchanges, he went on to accuse home affairs spokesman Mr Clegg of "flip-flopping" over his policies.
Mr Clegg said Mr Huhne was trying to create "synthetic differences" which "our opponents will use against us".
Days ahead of ballot papers being sent to Lib Dem members, Politics Show presenter Jon Sopel produced a briefing document with the words "Calamity Clegg" at the top, which he said had come from the Huhne camp.
Mr Huhne said he had not seen this and said he apologised if it had been written by one of his aides.
He added: "I don't support describing anyone else in the party as a calamity."
He said Mr Clegg had not established clear policies on nuclear weapons, and aspects of running schools and the health service.
Mr Clegg said: "I have said to you until I'm blue in the face that my position is very clear on all the issues... where what you are seeking to do is believe the worst that is said about me."
During exchanges in which the two men frequently interrupted each other, Mr Huhne said of Mr Clegg's NHS policy: "You are flip-flopping on this."
The acting leader of the Liberal Democrats, Vince Cable, told BBC 5Live the argument seemed typical of party leadership contests.
"From what I've heard so far it doesn't seem much worse than in most of the leadership contests that we've had in other parties as well as our own, so it's not a major departure I don't think," he said.
A spokeswoman for Mr Huhne said the title of the leaked document "Calamity Clegg" had been thought up by an "over-zealous researcher" and that he "completely dissociates himself from it".
The two men are the only contenders to replace Sir Menzies Campbell, who stepped down as Lib Dem leader last month after 19 months in the job.