Court of Appeal judges are considering legal issues involving a solicitor who worked for a billionaire businessman ordered to pay £453 million to his estranged wife.
Anthony Kerman, who had represented Farkhad Akhmedov at an early stage of proceedings, complained about an order made by Mr Justice Haddon-Cave during litigation in the Family Division of the High Court.
He complained that he had been unfairly summonsed to give evidence at short notice.
Lawyers representing Mr Kerman said the appeal raised important issues concerning "legal professional privilege".
Mr Akhmedov's estranged wife Tatiana Akhmedova was at the appeal hearing, which is expected to end later this week and is being held at the Royal Courts of Justice in London.
News of Ms Akhmedova's payout emerged during the summer of 2017 following a hearing in the Family Division of the High Court in London overseen by a High Court judge.
Mr Justice Haddon-Cave disclosed detail of the case in a written ruling published on a legal website.
His award was thought to be the biggest made by a divorce court judge in England.
A lawyer representing Ms Akhmedova told appeal judges that Mr Akhmedov had not yet "paid a penny".