Fernando Alonso left the door open for a possible return to Formula One on Thursday when he explained he was saying goodbye to the sport, but could not forecast the future.
The two-time world champion, who it is claimed turned down an offer from Red Bull before announcing his F1 exit, said: "I don't have a crystal ball to know the future. For me, it's a bye-bye, but who knows in the future."
Alonso rejected an offer from Red Bull before the team named Pierre Gasly as their 2019 replacement for departing Australian Daniel Ricciardo, who is moving to Renault next year, according to Sky Sports F1.
"Right now I am thinking that it is a goodbye, but life changes very quickly and life also taught me in the past how things may change in a couple of months' time or in years' time," said Alonso.
He told a news conference ahead of this weekend's Belgian Grand Prix that "it was a decision that probably I started thinking about last year.
"And then this year, 2018, there were a lot of changes into the team and with the engine manufacturer changes and things like that.
"I thought it was worth staying one more year. I enjoy driving these cars with new regulations, big tyres, more down-force and this year was some kind of joy to keep racing and to have another go.
"A couple of months ago, I decided it was the right time. I feel strong, feel a good level and want to say bye-bye to this sport when I am strong, not when I am not competitive or have no place to go.
"I prefer to take my own decision and take new challenges that Formula One cannot offer me at the moment."