Kattner is due to face questions as a witness on the fifth day of the hearing at the Federal Criminal Court in Bellinzona in Switzerland.

The German-Swiss official is among several witnesses called to speak at what is being billed as football’s trial of the century.

Others to have testified include Flavio Battaini, a former personal advisor to Blatter, and Peter Limacher, the ex-UEFA legislative office chief, as well as former Spanish Football Federation President Angel María Villar.

Federal prosecutor Olivier Thormann was also questioned as a witness where he said Kattner obtained information about a secret payment by FIFA to Platini.

Charges of fraud, embezzlement and corruption have been brought against Platini and Blatter due to a payment of CHF2 million (£1.6 million/$2 million/€1.9 million).

Former FIFA President Blatter has denied that he approved a fraudulent payment to his ex-UEFA counterpart, insisting it was part of a "gentlemen’s agreement" between them both.

Platini has also denied the charges.

Blatter told the court that the payment was for an "oral contract" the two figures made which dated back to 1998 when Platini became the 86-year-old's technical adviser.

Battaini and Limacher also confirmed that there was an early verbal agreement between Platini and Blatter.

The FIFA Ethics Committee banned Blatter and Platini for eight years in 2015 for the payment, which ultimately ended their administrative careers in football.

The sanctions were reduced to six years on appeal, but Blatter was then banned for another six years and eight months after being found guilty of several breaches of the FIFA Code of Ethics in 2021.

Blatter reigned as President of FIFA for 17 years, before falling from power due to numerous corruption scandals.

Kattner was banned from football for 10 years by FIFA in 2020 after being found guilty of conflicts of interest and abusing his position.

He was also fined CHF1 million (£830,000/$1 million/€950,000) by the adjudicatory chamber of FIFA's Ethics Committee.

The investigation into Kattner concerned amendments and extensions to contracts of FIFA employees, bonuses paid in relation to FIFA tournaments and the reimbursement of private legal costs.

It was launched in September 2016 and also investigated Blatter and ex-secretary general Jérôme Valcke for their roles in the illicit bonus and pay rise scheme.

Kattner had been sacked by FIFA in May of that year for "financial breaches", while Blatter and Valcke had already been banned from football when the investigation was launched.

FIFA's Ethics Committee found that the employment contracts of Kattner, Blatter and Valcke were amended to give them "extraordinary bonuses" in relation to the 2010 World Cup, 2014 World Cup and 2013 Confederations Cup.

Drafts of these amendments were found on a USB drive in Kattner's office.

Kattner's bonuses in relation to the three tournaments totaled CHF7 million (£6 million/$7.5 million/€6.5 million) - Blatter and Valcke received more.

After joining FIFA in 2003, Kattner was director of finance and administration from 2007 to 2015 and deputy secretary general for the same period.

He was also acting secretary general from 2015 to 2016.

A verdict in the two-week trial before a panel of three judges is expected to be reached on July 8, with sentences of up to five years in prison possible if Blatter and Platini are found guilty.