Renault Sport F1 boss Cyril Abiteboul acknowledges that there is some reliability risk involved with the upgrade, and thus the works team won't take advantage of any performance gains as it tries to consolidate its fourth place in the championship.

For that reason, it opted to give Nico Hulkenberg a Spec B when the German made a change this weekend at Spa.

However, the customers now have the option to take it at Monza or beyond if they want to gain a little performance – while accepting the reliability risks.

The situation is a new twist to the already complex and strained relationship between Red Bull and its engine supplier.

"We will not use it at Renault," Abiteboul told Motorsport.com. "Basically what we are doing is discussing with our customers who wants it. So it's available, and it's a step in power.

"It's coming with a couple of additional reliability risks, so basically we are leaving it up to the discretion of each team whether they want or or not, based on their sensitivity to the trade-off between power and reliability.

"At Renault we are more concerned about what's going on behind us, and therefore the risk of reliability, and an extra one tenth or two tenths is not going to make a difference because we are not going to catch Red Bull.

"Red Bull, they have nothing to worry about, nothing to lose, and that's why the sensitivity and the bias is slightly different."

Abiteboul confirmed that the team had the option to give Hulkenberg the new engine at Spa: "We could have had one available here for him, as a Spec C, that was a possibility."

Renault technical director Bob Bell confirmed that maintaining reliability was an issue for the team.

"We constantly have to trade performance against reliability," said Bell. "And it's often the case, where you can dial a little bit more performance and you raise reliability risk.

"And we make that decision and that affects where we introduce the upgrades to the engine. And for us, for the rest of this season, it's probably more important to be sure we finish the races than it is to get a little bit more performance."