"It was a contract I had with Platini, a gentleman's agreement," said the 79-year-old in an interview with Swiss media RROTV.
"It was implemented. I can't give any more details, the issue is being discussed in two investigations."
Asked directly if the contract had been made within the rules, Blatter added: "Yes, certainly, it was within the rules."
Blatter and Platini, 60, have both been suspended for 90 days by Fifa's ethics committee as Swiss authorities conduct a criminal investigation into corruption allegations at the scandal-tainted world football governing body.