Fernando Alonso has vowed he will win in Formula 1 in 2018 - even though the Spaniard still does not know for which team he will be driving.

After three years of frustration and disappointment with the ill-fated McLaren-Honda project, Alonso will make a decision on his future after the summer break, adamant his only criteria will be securing a race-winning seat.

"I will wait and make the best decision and whatever decision l will take it's because l will win in 2018," Alonso told Sky Sports F1 in an interview broadcast as part of the build-up to the Azerbaijan GP.

"Next year will be a happy year."

Sunday's race marks the first anniversary of the last time a driver - Sergio Perez of Force India - outside of Ferrari, Mercedes and Red Bull finished on the podium, a statistic which underlines the difficulty Alonso will face in landing a race-winning seat.

Mercedes are expected to retain Valtteri Bottas alongside Lewis Hamilton next season and Toto Wolff on Saturday all-but ruled out to Sky F1 the possibility of Alonso joining instead.

Red Bull, meanwhile, have also closed the door on Alonso after team boss Christian Horner insisted both Daniel Ricciardo and Max Verstappen are locked in for 2018.

And although a vacancy may emerge at Ferrari if Kimi Raikkonen departs, many in the paddock doubt the feasibility of Alonso returning there just three years after quitting the team.

But, in an intriguing aside, Alonso told Sky F1 at the start of the weekend that he is confident doors which currently appear to be shut will open up for 2018.

"I know there are a few options out there and there are more options than people are talking about now, there will be some surprises," Alonso told Rachel Brookes. "We will see."

The Formula 1 Gossip column

Out of contract at the end of the year, Alonso's future has become a hot topic of speculation in the paddock as the two-time world champion considers his options. Also linked with a return to Renault, where the Spaniard won both of his two championships, the prospect of Alonso staying at McLaren cannot yet be ruled out either.

But having said he will not take any "gambles" on his 2018 choice, Alonso could still leave McLaren even if, as anticipated, they rejoin forces with Mercedes at the expense of struggling Honda.

"Not necessarily," Alonso responded when asked if a McLaren-Mercedes deal would persuade him to stay. "It's not 100 per cent sure what l will do. My decision doesn't depend on which engine we have."

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