Blatter served as FIFA President from 1998 to 2015, with Platini widely seen as his protege.
Former FIFA officials Sepp Blatter and Michel Platini have gone on trial in Switzerland for alleged corruption after more than six years of criminal proceedings.
The two men each face up to five years in prison if found guilty but are more likely to be handed suspended sentences.
Blatter’s 17-year reign as FIFA president came to an end in June 2015, when he resigned amid a corruption scandal.
A few months later, federal prosecutors in Switzerland unveiled their investigation into a 2 million Swiss francs (€1.98 million) payment that FIFA made to Platini in 2011.
Swiss prosecutors have argued that the payment was made without legal basis "damaging FIFA's assets and unlawfully enriching Platini".
The FIFA ethics committee banned both men from football, ending Platini's campaign to succeed his former mentor and also removing the 66-year-old as president of UEFA.
Both men have long denied wrongdoing and claim they had a years-old verbal agreement for the money in return for Platini's consultancy work between 1998 and 2002.
Blatter was seen smiling as he entered the Federal Criminal Court of Switzerland in Bellinzona on Wednesday.
“Absolutely, absolutely, absolutely,” he told reporters when asked if he was confident about his chances.
“I feel optimistic, like always ... If I didn’t feel confident the first day that would be bad. I am very confident.”
"Football is me. It’s been 45 years that I’ve been serving FIFA and international soccer. And it’s my life, it’s my professional life,” Blatter added.
The 86-year-old was due to answer questions in court on Wednesday but delayed his testimony due to chest pains.
The former FIFA president has been charged with fraud, mismanagement, misappropriation of funds and forgery of a document, while Platini is accused of fraud, misappropriation, forgery and as an accomplice to Blatter’s alleged mismanagement.
The suspects' lawyers have tried to broaden the case to include alleged corruption involving FIFA's current president Gianni Infantino. Prosecutors have dismissed any connection between the two cases as a "conspiracy theory".
The two-week trial is expected to continue until June 22, with a verdict due on July 8.