Federer, 37, is not expected to play beyond the 2020 Tokyo Olympic Games.
But there are suggestions he could call time on his illustrious career if he clinches a 21st Grand Slam title – potentially on his preferred surface at Wimbledon.
However, Federer has admitted he could decide mid-match that his time at the top of the sport is over.
“As a professional athlete, you want to be able to stop when you decide,” Federer told El Pais.
“It can be something that you decide during the holidays.
“It could be that you say: I have had enough; You give a press conference and let go.
“Or you might be playing a match and say, ‘We’ve come this far’.”
Federer is currently trying win the Madrid Open on his first return to clay in three years.
The Swiss star takes on Dominic Thiem in the quarter-finals this evening but he is unsure how many more occasions he will grace the red dirt.
“I think as long as it’s your own decision, it’s perfect,” Federer added.
“The where, how or when can grow inside you.
“I’m not looking for a fairytale ending.
“There are many people who think that my career should end with a perfect ending.
“But I think that’s the wrong approach. That would be a disappointment.
“If I had been looking for a fairytale ending, I would have had the opportunity several times. But I’m relaxed and flexible in this regard.”