Fernando Alonso's troubled relationship with Honda is facing fresh scrutiny after McLaren's Japanese engine partner hinted he may have retired from the Belgian Grand Prix on purpose.
Alonso, the 36-year-old two-time champion who is out of contract with McLaren at the end of the season, cut an increasingly frustrated figure throughout Sunday's race at Spa-Francorchamps.
The Spaniard was as high as seventh following an impressive opening lap, but McLaren's under-powered Honda engine left him exposed, and he soon dropped out of the points.
Alonso described the situation as "embarrassing" over the team radio before he pulled out of the race altogether on lap 27, citing an apparent engine problem.
Alonso's retirement, his seventh of a miserable year, came only moments after he had been informed that rain was not forecast for the remainder of the race, and thus ruling out the likelihood of scoring any points.
And to add further intrigue and suspicion, Honda then revealed that there was not an obvious fault with Alonso's engine.
"After starting brilliantly, Fernando then had a tough race overall," Honda boss Yusuke Hasegawa said.
"He radioed in with what he thought was a problem with the car, and although there was nothing showing in the data, we decided to stop the car as a precaution."
Alonso has been highly critical of Honda throughout his second spell at McLaren, and claimed after qualifying in Spa that the British team would have locked out the front row if they had a more powerful engine.
He qualified 11th, while his team-mate Stoffel Vandoorne was thrown to the back of the grid following a series of engine penalties.
"For sure, it is not easy to race like this, as you cannot have any good wheel-to-wheel battles," Alonso said. "It was a difficult afternoon and we were not competitive in race trim.
"The car was too slow on the straights and it was impossible to have any battles out there, so points were also impossible today. Eventually, we had to stop due to an engine issue."
McLaren's relationship with Honda is at breaking point after three seasons of disappointing results. The Woking-based team have staged talks with Renault over an engine deal for 2018.
Alonso, meanwhile, insists he is not in a rush to determine his future after Williams emerged as a surprise contender to land the double world champion's signature.
Mercedes and Ferrari are not interested in Alonso, while Red Bull's line-up of Daniel Ricciardo and Max Verstappen will remain unchanged for next year.
"I received several offers," Alonso said ahead of Sunday's race. "To 60 per cent of those offers I say no right away, the other 40 per cent are still on the table. I will wait as long as possible."