2018 French GP: Sebastian Vettel addresses the challenges of the Paul Ricard Circuit. Seb previews the next race.

Sebastian Vettel is expecting Mercedes to be a serious threat at the French Grand Prix regardless of whether it is able to run its latest engine upgrade.

Mercedes made a last-minute decision not to introduce its planned engine upgrade ahead of the Canadian Grand Prix due to reliability concerns, meaning all Mercedes-powered cars had to use the same hardware they had used at the previous six races.

Back at Mercedes’ power unit base in Brixworth, the engine upgrade has been undergoing development work all week with the aim of bringing it to this weekend’s race in France, but on Thursday Mercedes was still deliberating on whether to run it.

Because drivers are limited to three engines per season, another failure to deliver the upgrade in France would mean all Mercedes-powered cars would have to take a fresh version of the original specification rather than the upgrade.

But Vettel doubts the performance gain from the upgrade would be enough to make a big difference in the battle at the front of the field.

“I can’t speak on their behalf and I don’t know how big the step was, going to be, or is going to be — if it’s a lot of power, then probably yes [it will make a difference], if it’s not then probably it doesn’t make a difference.

“I think we’re progressing throughout the year, if you look at the car, if you look at the power units, obviously we don’t have that many chances to introduce new engines, and even if we had it’s not that easy to make huge progress so I’d be surprised if it would have such a deep impact.”

Vettel said it would be wrong to focus solely on the engine performance when car development can also impact on the competitive picture from race to race.

“I believe they’re very strong no matter what, and as I said before, some races suit you a bit better for some reasons and others don’t, for example the advantage they had in Barcelona even if they stay with that engine, with that advantage they’ve had in that race, we can all put a lot of horsepower, a lot of downforce and our car still would lack pace compared to them.

“Now, is it all in the car? All in the engine? I don’t think so. I think it’s a combination of things. They had obviously a great weekend there and everybody else was a little bit behind. Other weekends it’s been the other way around so we’ll see how it’ll be this week and then the weeks after.”