In an interview with Fox News on Monday, Mr Trump’s personal lawyer said there were “four people” who could vouch that Lev Parnas’s account of the meeting during a 2018 White House Hannakuh party was untrue.
Mr Giuliani told presenter Laura Ingraham: “[He said there were] four people in that meeting. The four people in that meeting – myself, his former partner Igor Fruman and two others – say that it’s absolutely untrue, the meeting never took place.”
In a previous interview on the same network, the former New York City mayor told Ed Henry there were “five witnesses … who all say categorically untrue”. Aside from Mr Fruman, he did not name the witnesses.
Both Mr Parnas and Mr Fruman are Republican donors who were charged last year with campaign finance offences over allegations they worked to “funnel foreign money to candidates for federal and state office”.
They were thrust into the impeachment probe when Mr Parnas agreed to co-operate with inquiries into allegations the US president withheld aid to Ukraine to pressure the country into investigating conspiracy theories about his Democrat rival Mr Biden.
Last week Soviet-born Mr Parnas, a long-time associate of Mr Giuliani, insisted Mr Trump knew about his efforts to dig up dirt on the former vice-president. He told MSNBC's Rachel Maddow: "President Trump knew exactly what was going on."
In Mr Giuliani's latest interview with Fox News, he said he was "heartbroken" by what he depicted as a betrayal by his associate, who is the godfather to his son.
"Obviously, I was misled by him," he added.
The interview came as Mr Parnas called for attorney general William Barr to remove himself from overseeing his criminal case over what he said were conflicts of interest.
“It is in the public interest to remove this matter entirely from the Department of Justice,” his lawyers wrote to Mr Barr.