Former world champion Carl Frampton has dishonestly claimed ex-manager and promoter Barry McGuigan withheld earnings, the High Court heard on Tuesday.
Counsel for Mr McGuigan accused the Belfast fighter of lying about profit arrangements as part of a bid to blacken his client’s name.
Liam McCollum QC said: “A vast amount of the assertions he makes are in fact inventions.”
Counter-allegations emerged during submissions on the costs of a preliminary hearing to determine the appropriate jurisdiction for the legal battle.
Earlier this year a judge ruled that Mr Frampton’s action will be heard in Belfast.
He is suing Barry McGuigan, his wife Sandra McGuigan and Cyclone Promotions (UK) Ltd, alleging a failure to pay purse money from his bouts.
The writ forms the basis of Mr Frampton’s counter-claim to separate proceedings brought against him by the McGuigan family-run Cyclone Promotions at the High Court in London.
The 31-year-old former two-weight world champion split with Cyclone last year.
He is facing an action from his former promoters for alleged breach of contract.
The Tigers Bay-born fighter is counter-suing on a number of grounds, including an alleged appropriation of fight earnings and a breach of the terms of an International Promotional Agreement (IPA).
His lawsuit refers to contracts for bouts in Northern Ireland, England and the United States.
It involves claims against now dissolved Cyclone Promotions UK Ltd, of which Mr and Mrs McGuigan were directors, over purse fees, broadcasting rights, ticket sales and merchandising from Mr Frampton’s second world title match against Leo Santa Cruz in Las Vegas in January 2017.
During the initial hearing on jurisdiction it was alleged that Mr Frampton’s deteriorating relationship with his former manager and promoter ended after the taxman called at the boxer’s home about a company VAT bill for almost £400,000.
By the time they parted the boxer believed Mr McGuigan was “ripping him off and concealing it”, the court heard.
Mr Frampton also said the cracks first appeared when he was allegedly “fobbed off” about being paid after defeating rival Scott Quigg in Februay 2016.
In a sworn statement he accused Mr McGuigan of abusing the trust he placed in him to look after his career.
Lawyers for the McGuigans insisted all of the allegations are categorically denied.
In court counsel hit back at the fighter’s claims and how they were made at a preliminary stage in the action.
“The plaintiff... tried to advance the whole merit of his case, mostly in an attempt to blacken my client’s name before the press,” Mr McCollum contended.
“That was the main agenda behind the vicious attack on my client.”
Sitting at the back of the courtroom, the boxer heard the barrister set out an intention to refute his claims at trial.
“It will be our case that a lot of the contentions made by Mr Frampton are lies and dishonest,” he said.
“The whole basis of his case, for example a 30% share of the profits of promotions, is simply dishonest.”
Mr Justice Horner was told it had been a deliberate tactical decision by the McGuigans not to go into the full details of the merits of their defence during the preliminary jurisdictional hearing.
According to their lawyer that was not only felt to be an inappropriate time to do so, but would also create difficulties for the ongoing case.
“We decided we would not embark on a mud-slinging exercise at this stage,” Mr McCollum said.
Arguing that costs should be reserved until the end of the trial, he added: “The plaintiff should not be rewarded for the way they continually tried to malign my clients.”
Gavin Millar QC, for Mr Frampton, contended it would be unfair for the fighter to have to wait to be reimbursed after securing the right to have his case heard in Belfast.
He said: “The defendants have failed in their attempt to prevent us litigating here, and we should be entitled to the costs we have had to incur to get this litigation in this jurisdiction to the starting post.”
Mr Justice Horner reserved judgment on the costs issue.