The Thatcherite candidate allegedly received three suits costing £11,000 (€13,000) Franco-Lebanese lawyer Robert Bourgi last month.
Although he denied any wrongdoing, Mr Fillon admitted he made an “error of judgement” and claimed he had returned the tailor-made Arnys suits.
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But investigators now believe two suits he “gave back” to Mr Bourgi may not be the ones he received.
Eric Moutet, a lawyer acting for Mr Bourgi, told French media: “They did not appear to be Arnys suits.
“In the pocket of one, there was a ‘Made in Holland’ label.”
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Mr Fillon's chances of winning the presidency have been badly hit by continuous allegations
He also said Mr Fillon had returned a blazer and a pair of trousers made by Arnys, which Mr Bourgi gave to him in 2014.
Mr Bourgi claimed Mr Fillon’s campaign pressured him to keep quiet over the scandal after it was revealed.
He initially denied giving the suits to Mr Fillon, but admitted doing so once the scandal came to light.
Mr Bourgi said it was annoying “to have had to lie about the gifts for a week”.
But he also claimed the gifts involved neither “conflicts of interest nor insurance-peddling”.
Previously the frontrunner for the French presidency, Mr Fillon suffered a spectacular downfall in February over allegations he had paid his family members some £760,000 (€900,000) of public money for work they did not do.
He came under fire in February over allegations of nepotism
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The conservative candidate has denied any wrongdoing.
Express.co.uk has contacted to Mr Fillon's campaign for comment