Mr Mills denies taking a bribe from Mr Berlusconi
Prosecutors in the appeal case of UK tax lawyer David Mills have opposed a defence request for the Italian prime minister to appear as a witness.
The estranged husband of UK minister Tessa Jowell was convicted of accepting a large bribe from Silvio Berlusconi.
Mr Berlusconi had been shielded from prosecution by a law he proposed, but this week judges overturned it.
Ansa news agency said prosecutor Laura Bertole told the court Mr Berlusconi knew "nothing" about the matter.
"Silvio Berlusconi told the press 'I don't know this David Mills'. He therefore claims to know nothing" about the matter, Ansa quoted Ms Bertole as telling the court in Milan.
David Mills is appealing against his conviction in February of accepting a £400,000 bribe from the Italian PM, for which he received a jail sentence of four and a half years.
Ms Bertole asked the court to confirm the sentence against Mills, who has protested his innocence in what he calls a "highly political" case.
Mr Mills is unlikely to serve any prison sentence because Italy's statute of limitations means the case will soon expire.
Mr Berlusconi introduced an immunity law soon after taking office in 2008
Mr Mills, who separated from former culture secretary Tessa Jowell in 2006, was one of Mr Berlusconi's consultants on offshore tax havens.
In his trial the prosecution alleged Mr Berlusconi paid Mr Mills for not revealing details of offshore companies during two previous trials in 1997 and 1998, in which the lawyer gave evidence as an expert witness.
The charges stemmed from a letter which Mills sent to a British accountant in 2004 in which he said the £400,000 payment came from "Mr B".
Mr Mills initially admitted having received money from Mr Berlusconi "in recognition" of the evidence he gave, but later said the money had come from an Italian shipping magnate, Diego Attanasio.
Mr Berlusconi has denied making any such payment to Mr Mills.
This week Italy's top court ruled that a law that granted Mr Berlusconi and other top officials immunity from prosecution while in office was unconstitutional.
The Mills case was one of three corruption and tax fraud that were frozen because of the immunity law, but the judges' decision has paved the way for them to resume.
As of earlier this year, Mr Berlusconi had been involved in 2,500 hearings, had received 587 visits from the police and had spent 174m euros (£155m) in legal fees during his political career.
In some cases he was found guilty of several charges of illegal party financing, corruption, bribery and false accounting - but he always won on appeal, thereby avoiding jail.
On Friday he described himself as the most persecuted person "in the entire history of the world".