Claire Thibout, the former accountant, said that she had been involved in withdrawing $200,000 in cash to be given to Eric Woerth, the country's labour minister, in unmarked envelopes as a donation to Sarkozy's 2007 election campaign.
An official investigation cleared Woerth on Sunday of abusing his position to shield France's richest woman from a tax audit, but critics said the report did not erase suspicions of a conflict of interest.
Woerth was treasurer of Sarkozy's 2007 presidential campaign, remains treasurer of the UMP and served as budget minister who was in charge of tax affairs, and his wife worked for Bettencourt's wealth manager.
Woerth said on Monday that he would consider resigning from his job amid the scandal.
|Woerth, right, has said he would consider resigning from his labour minister post [EPA]
Sarkozy will give the rare television interview a day before Woerth presents to the cabinet a pension reform, which is unpopular with voters and unions.
Seeking to silence criticism, the government's investigation report concluded that Woerth played no role in the tax affairs of the Bettencourts, their wealth manager or family friends.
The budget ministry said inspectors had found that Woerth neither interfered with the handling of Bettencourt's tax file nor neglected to follow up evidence of possible tax evasion.
However, the report did not cover the allegations that Woerth was given an illegal donation for Sarkozy's campaign.
Police are investigating her statements, which Patrice de Maistre, the wealth manager, has denied.
Despite calls for Woerth to resign, or for Sarkozy to bring forward a cabinet reshuffle planned for October, the president seems determined to tough it out in the hope that the story will die away.