Former FIFA president Sepp Blatter fought to overturn his ban from football in a marathon, 14-hour appeal hearing on Thursday, in a long-shot bid at redemption after his career ended in disgrace.

Blatter mounted his defence against the six-year FIFA suspension imposed over ethics violations at the Court of Arbitration for Sport (CAS), which typically has the final word in major sport disputes.

Engulfed by corruption scandals since May of last year and the target of a criminal investigation in his native Switzerland, the 80-year-old Blatter appeared upbeat after emerging from the courthouse well into the night.

"It's a long day," Blatter said at 10:35 pm (2035 GMT). "I cannot give any prognosis how it will be decided."

He entered CAS shortly before 8:00 am wearing a dark navy suit and sporting some light stubble, telling reporters he remained "optimistic" and had confidence in the arbitrators.

The case that triggered Blatter's downfall first emerged in September of last year, when Swiss prosecutors said they were investigating him over a suspect two million Swiss franc payment ($2 million, 1.8 million euros) he authorised in 2011 to his one-time heir apparent, Michel Platini.

Blatter has insisted the payment was part of a legitimate oral contract, a claim that has been rejected in multiple hearings at FIFA's in-house courts.

World football's former most powerful man said he would respect the CAS decision, which should be delivered within weeks.

"I will accept the verdict," Blatter said before the hearing.

"I do hope it will be positive for me, but we are footballers. We learn to win but also we learn to lose," he added.

- Platini testifies -                   

Platini, the former head of European football, was also sanctioned by FIFA over the funds.

The Frenchman lost his CAS appeal in a May verdict that likely diminishes Blatter's hopes of victory.

Speaking to reporters before giving evidence at Thursday's closed-door hearing, Platini said Blatter's fate may already be sealed.

"I'm not sure if a decision hasn't already been made," he said, vowing to tell the truth about the infamous payment "for the umpteenth time."

Platini left CAS after testifying at around 4:30 pm, but made time for some mild mocking of Blatter's stubble.

"Mr. Blatter is a little tired. He has a beard, so I'll send him a razor," the ex-UEFA boss said.    

- Settling a debt? -                   

Blatter restated his claim that he authorised the payment because FIFA owed Platini money.

Platini had been hired by FIFA as a consultant from 1999 to 2002 and had apparently not received his full compensation.

"I am sure, at the end... that the panel will understand that the payment made to Platini was really a debt that we had" with him, Blatter said Thursday. 

"This is a principle: if you have debts you pay them."

FIFA's ethics committee was not convinced by the explanation, banning both Blatter and Platini for eight years in December. Those suspensions were however cut to six years on appeal in February.

CAS however judged FIFA's sanctions against Platini "too severe" and trimmed his suspension to four years.

That outcome would likely offer little comfort to the ageing Blatter, whose four-decade career as a football broker is likely over.

Separate from the Platini case, Swiss prosecutors are also investigating Blatter over alleged mismanagement during his 17-year tenure as FIFA president.

He was replaced in that job by fellow Swiss national and former UEFA number two Gianni Infantino in February.

An investigation commissioned by Infantino's administration also accused Blatter and two top deputies -- Jerome Valcke and Markus Kattner -- of awarding themselves nearly $80 million worth of improper salary increases and bonuses during their final five years in office.

Both Valcke and Kattner have been sacked by FIFA. Valcke is also the subject of a Swiss criminal probe.

Blatter and Platini were the most prominent casualties during more than a year of unprecedented scandal that upended world football, but many others have fallen.

Prosecutors in New York have indicted 40 football and sports marketing executives over allegedly receiving tens of millions of dollars in bribes and kickbacks.