However, rumours circulated in local Swiss press yesterday that the world No 2 had signed a bumper 10-year deal with Uniqlo.
Federer had apparently penned a $30m-a-year contract (£22.4m) to represent the Japanese brand, who severed their ties with Novak Djokovic last year.
The 37-year-old says he has not yet decided which sports brand he will represent for the remainder of his career.
But Federer admitted he could still sign an extension with Nike - if the deal is right for both parties.
"It has already expired in March and we are in negotiations,” Federer said.
"They are rumours and nothing is ruled out, neither my continuity in Nike nor the end of our collaboration, nor a change to any brand.”
Although now out of contract, Federer has been snapped wearing Nike clothing at the Stuttgart Open.
The Swiss star is hoping to return to the top of the world rankings by winning his opening three rounds in Germany.
Rafael Nadal is the current world No 1 and he retained his title after victory in the French Open final yesterday.
The Spaniard beat Dominic Thiem in straight sets to secure his 11th Roland Garros title.