Red Bull Team Principal Christian Horner has slammed engine supplier Renault over poor reliability following Max Verstappen's third retirement of the season due to a failure at the Belgian Grand Prix.

Speaking after the race, the Dutchman claimed luck was no longer a factor in the problems and is now expected to take a grid penalty at this weekend's Italian Grand Prix at Monza following what was his sixth overall failure to finish in 2017 at Spa.

It is just the latest in a number of criticisms this season and, commenting on the situation, Horner echoed comments Verstappen made earlier in the year by suggesting the French manufacturer isn't in a position to fight for wins and championships.

"Renault are quite aware that its reliability and product isn't where it should be," he said. "It's their business to sort that out. We're a paying customer and it's obviously below par the service we are seeing at this point in time because [of the] reliability issues, the failures.

"We pay a hell of a lot of money for the engine they need to sort it out. It's hurting them as much as it is hurting ourselves and at this level, you can't afford the kind of failures that we're consistently seeing."

The Briton didn't just limit his disappointment at Renault to Red Bull either, pointing out the problems at junior team Toro Rosso this season and at Spa.

"Reliability across the three teams is pretty dire," he claimed. "Turbo failures with Kvyat, engine replacements that have had to happen with two cars as we come here. It's not great, it's far from great and it's not the level an engine supplier which wishes to be competitive in F1 should be at.

"They are working hard at it and hopefully putting in place process to avoid the kind of issues that we are seeing."

The ongoing problems once again will cause speculation over Verstappen's future with Red Bull, with the 19-year-old admitting patience is running thin.

“It’s enormously frustrating but you got to take a bigger view you can’t get caught up,” Horner responded. “Here and now it really hurts, and it really hurt Max because it’s his home race, massive crowds, huge support, he’s in a great position, and his engine has failed on him. That’s hugely frustrating for him and of course the support group that he has around him.

“That needs to change but unfortunately as a team that’s something we don’t control. It’s beyond our control. So all we can do is put pressure on our supplier, like any supplier, to say ‘come on, get your act together!”