McLaren boss Andreas Seidl has expressed frustration at Renault's continued lack of reliability after issues for both drivers at Spa.

Carlos Sainz would grind to a halt after just one lap, having also suffered a very bad launch at the start, with Lando Norris' engine giving up just one lap from the end while running in fifth.

Poor reliability has continued to be the weakness of Renault despite the strong power gains they have made this year, and after this latest setback, the McLaren chief is left wanting answers.

“It’s disappointing for us to have two DNFs, with one driver not even being able to make the race start,” the German said post-race. “At the same time, the situation is on Renault’s side as well.

“Renault is making a huge effort in order to bring power updates throughout the season so that’s encouraging to see, but of course, [it is] disappointing to have all these penalties and the DNFs in the races.

“It is important that we have a transparent and open relationship there, and that we analyse the issues and try to solve them together.”

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It is understood that McLaren reverted to an older spec engine for the race, having not received the latest update that Renault had for their works team.

But Seidl doesn't think that engine wear played a role.

“We need to wait first, I don’t think it’s related," he said. "Again, it’s speculating and we really need to see. I don’t think it’s related to the engine spec.”