Mr Warren, 40, of Tewinwater, Hertfordshire, is suing Mr Marsh, 34, the former world light welterweight champion, for damages over what he called the 'very grave and wounding' libel on Thames Television's Midweek Sports Special in January 1989.
He told Mr Justice Drake and the jury at the High Court in London that he was 'stunned and puzzled' by a story in the Sun on 14 September 1987, that said Mr Marsh was leaving boxing because he had been diagnosed as suffering from epilepsy.
He thought it was a 'nonsense' as the day before Mr Marsh had signed a contract to fight Frankie Warren, an American, for a purse of dollars 250,000 ( pounds 155,279) and had not given the 'slightest indication' he would not be able to honour that commitment.
Mr Warren told of a meeting with Mr Marsh and a Sun journalist later that week. 'The Sun's journalist inferred I knew Terry had epilepsy. I got very irate and the journalist and I nearly came to blows. Terry got in the middle and said 'calm down'. He said in front of the reporter that I never knew about it. I asked the journalist to leave us alone and I just tried and tried to get an explanation from Terry why he hadn't told me about the illness or about the Sun running this story. He just looked sheepish and never answered.'
Fourteen months later the two men were interviewed for television when Mr Marsh was trying to get back his boxing licence on the basis that new medical evidence attributed his blackouts not to epilepsy but to eating eight or 10 Mars bars after a fight. During his interview Mr Marsh said he could not comment on a question about whether he had told Mr Warren before his retirement that he had epilepsy and he was 'packing in'. Asked whether he was saying he had told Mr Warren, Mr Marsh replied: 'I told everybody who needed to know.'
Mr Marsh, of Lee Chapel South, Basildon, Essex, denies libel and says his television comments were true. He claims he had told Mr Warren about the epilepsy diagnosis on two occasions before the contract was signed.
The hearing continues today.