Michel Platini's lawyers say a memo published in a French newspaper on Sunday could help clear the suspended Uefa president of wrongdoing.
Platini and Fifa president Sepp Blatter have been suspended over allegations a "disloyal payment" was made to Platini in 2011 for work done years earlier.
Le Journal du Dimanche says the memo, dating back to 1998, includes a payment agreement between Platini and Fifa.
Platini's lawyer Thomas Clay called the 23-page document "important evidence".
Clay, speaking to the Reuters news agency, added: "From the moment that we have proof of an agreement between Fifa and Mr Platini, and of knowledge of this agreement by officials of Uefa, then this inquiry falls down.
"For us, it's very important evidence that Mr Platini has always been telling the truth."