Fifa president Sepp Blatter and European football chief Michel Platini are facing an investigation by Fifa's ethics committee.
The move comes after the Swiss attorney general opened criminal proceedings against Blatter, 79.
He is accused of signing a contract "unfavourable" to world football's governing body and making a "disloyal payment" to Uefa president Platini, 60.
Blatter denies wrongdoing and his lawyer says he is co-operating fully.
The ethics committee is looking into the circumstances of a payment of two million Swiss francs (£1.35m) that Platini received in 2011 for work said to have been carried out more than nine years previously, reported the Press Association.
Swiss prosecutors opened criminal proceedings against Blatter on Friday.
Platini - who worked as Blatter's technical advisor between 1999 and 2002 - was interviewed as a witness by officers from the attorney general's office.
The Frenchman is yet to explain the nine-year delay in payment but he too denies any wrongdoing.
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