Red Bull duo on penalty bubble as Renault changes MGU-H

All three had taken a fourth example of the MGU-H on Saturday, which means that the next new one will automatically trigger a 10-place grid penalty.

Hulkenberg's Renault teammate Jolyon Palmer took a fourth MGU-H the day before. Haas pair Kevin Magnussen and Romain Grosjean have also taken their fourth turbos this weekend.

With Sebastian Vettel having used a fourth turbo several races ago, there are now seven drivers just one change away from grid penalties - not counting McLaren pair Fernando Alonso and Stoffel Vandoorne, who have been stuck in a cycle of penalties for some time.

While taking a fourth power unit element doesn't mean that older versions can't be used, the fact that there are still 11 races to go suggests that all those currently on the bubble will at some point have to face penalties.

The Renault change was prompted by a problem experienced on Friday by Ricciardo, which forced an overnight modification.

"After Baku we had a number of things to improve on the reliability side," Renault Sport boss Cyril Abiteboul told Motorsport.com.

"We've done lots of changes. It has been two weeks that have been extremely intensive for us, just like the previous weeks have been extremely intensive from the performance perspective, this time around we need to focus on reliability.

"It meant a lot of changes to the technical definition, and sometimes when you work in a hurry you don't have time to do all what you are supposed to be doing in terms of sign-off. There was one particular decision made on the MGU-H where we hadn't had the time for it to be signed-off.

"We tried something, it was really on the limit of introducing or not introducing that modification.

"Indeed it created an issue on one of the cars only, Ricciardo's, and that issue meant that we took the decision to change all the others. We tried something and we had the capacity to react overnight, and hopefully this will not repeat again."

Abiteboul confirmed that, because the change is not related to parts frozen under the FIA rules, previously used MGU-Hs can now be modified and returned to race weekend use.

"The issue we had on the MGU-H yesterday we will be able to patch or modify back at the factory and use it again because it's peripheral, it's ancillary."

It's understood that the Toro Rosso drivers are using an older MGU-H spec, which didn't have to be changed.

Meanwhile, Red Bull boss Christian Horner conceded that grid penalties look inevitable for his drivers.

"It's not ideal," he told Motorsport.com. "But just looking at Sebastian's allocation, it looks pretty similar to be honest. It is what it is.

"We're not quite at the halfway stage yet, but we'll do our best to manage it between now and the end of the year. A couple of the old ones are still alive."

Teams often introduce new power unit parts at Spa in preparation for the high speed double-header with Monza, while the nature of races at the Belgian track mean it's possible to make up ground from a poor grid position, making it a logical venue for a change.

Asked if there was a chance that Verstappen could face a grid penalty in front of a large crowd of Dutch fans at Spa, Horner said: "Hopefully not. It depends if you've got the choice. Monza is an obvious place as well."