France sent the African champions out of the World Cup with a 2-0 win in Brasilia on Monday and after the game, Keshi was quoted as saying: "It's time for me to go back to my family and face fresh challenges."
The Big Boss was also reported to have informed his players in the dressing room about his decision, but the football federation says he has not sent them a letter yet.
"Coach Keshi has not submitted an official resignation letter," a NFF spokesman told Goal on Tuesday.
"He was not employed in the mixed zone [after the France game] or on Facebook."
Keshi took over from Samson Siasia in 2011 and previously resigned after the Africa Nations Cup last year, before he was persuaded to continue.
Thanks
