Fernando Alonso has thrown his McLaren future into doubt after claiming he is unsure whether he will still be at the beleaguered British team in 2016.

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Alonso was ninth in the opening stages of the Japanese Grand Prix, but the Spaniard and his equally frustrated team-mate Jenson Button fell back through the pack as their Honda-powered cars struggled to compete which has been the story of a disastrous season so far.

“I am getting passed down the straight like a GP2 – this is embarrassing, very embarrassing,” said Alonso over the team radio.

Moments later after Max Vertsappen, 17 years Alonso’s junior, sailed round the outside of the double world champion at turn one, he yelled: “GP2 engine. GP2. Arggh.”

It was a damning, and very public, swipe at Honda from a driver who has spent much of this season towing the party line.

Earlier this week, Alonso’s former Renault boss Flavio Briatore claimed the Spaniard would quit McLaren if they fail to provide him with a winning package.

On Saturday Alonso, who is in the first of a three-year deal with McLaren, refuted those suggestions, saying he will “definitely” be with the British team next season.

But after he finished 11th in yesterday’s race, Alonso, when asked by the BBC if he would still be in the sport next year, said: “I don’t know. There are still five races to go and we need to improve the situation and make sure we are competitive and we are on top of our problems. It will not improve by Abu Dhabi and the remaining races will be tough.

“Next year’s project is what we are looking for, and my intention is to stay and win. I am sure we will win together but the matter is when and we need to make this tough time as short as possible.”

McLaren’s CEO Ron Dennis emerged from his sick bed yesterday after being struck down by a virus to face the media and head off any suggestion that his team is in crisis.

In response to Alonso’s claim that he could leave McLaren at the end of the season, Dennis replied: “I spoke to him earlier today. He has got a contract. He understands the contract and I am surprised at the comment.”

Dennis, who confirmed Alonso does not have a breakout performance clause in his McLaren deal, was also unhappy with his driver’s very public radio rants.

The Spaniard’s comments will be of deep humiliation to Honda at their home race with their top executives in attendance.

“I am not going to condone those sort of things because it does not show the professionalism that I would like all of our drivers to show,” Dennis said.

“He is in the car. He is frustrated and of course his exposure is to the technical staff which is not particularly a constructive way to communicate with everybody at Honda.

“The way for me to deal with drivers is either through the appropriate management channels in Eric Boullier or in certain circumstances to talk to them myself. But whatever I choose to do, or however it is done, remains a team matter.”