Alonso had endured a frustrating afternoon at Spa-Francorchamps, as he slipped down the field thanks to a lack of straightline speed.

His unhappiness at the situation was highlighted in a series of radio messages where he made clear that the lack of power he had was hard to accept.

"Embarrassing, really embarrassing," Alonso said on the radio at one point. That was followed by "I really don't care too much about the gaps. This is just a test."

After falling out of the points and towards the back of the field, Alonso then asked the team about the possibility of any downpour before the end of the race, which could have given him an opportunity to grab a good result.

However, the team was quick to respond that there was no rain showing on the radar.

Shortly after that message, Alonso slowed and came in to the pits after reporting: "Engine problem. Engine problem."

Honda has suggested, however, that there was nothing wrong with the power unit, prompting conspiracy theories that Alonso had retired on purpose.

Honda F1 engine chief 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 remained adamant, however, that he had stopped because of a failure.

"For sure, is not easy to race like this, as you cannot have any good wheel-to-wheel battles. 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."