Lawyers for the former French Prime Minister, Dominique de Villepin, say they will sue President Nicolas Sarkozy for having called him "guilty".
Mr Sarkozy is accused of violating the principle of presumption of innocence.
Mr de Villepin, an arch-rival of Mr Sarkozy, went on trial on Monday over the so-called "Clearstream" affair.
It is alleged that Mr de Villepin tried to manipulate a judicial investigation to hurt Mr Sarkozy's chances of winning the 2007 presidential election.
Asked for a comment on the trial, Mr Sarkozy told French television on Wednesday: "After a two-year investigation, two independent investigating judges ruled that the guilty parties should be tried before a criminal court."
Correspondents say that, as president, Mr Sarkozy enjoys immunity from prosecution, but that the defence team may use the "guilty" comment to bolster an appeal on behalf of Mr de Villepin. They could argue that Mr Sarkozy is using political influence to pervert the course of justice. read more
