Sebastian Vettel says he would be very surprised if Mercedes were able to make "huge progress" with its engine upgrade.
A decision is still yet to be made if Mercedes will unleash their engine upgrade this weekend in France.
Vettel, who now sits at the top of the drivers' championship, had his Ferrari engine upgrade in Montreal and consequently won the race.
The German driver says that he doubts Mercedes' engine upgrade will make too much of a difference.
"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 progress," Vettel explained to Crash.net.
"I'd be surprised if it would have such a deep impact.
"It depends. 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, if it's not then probably it doesn't make a difference."
There has been speculation about whether Mercedes' upgrade will be delayed even further and Vettel was speaking about whether this scenario would have an impact on the title race.
"I don't know if that's speculation or if that's true, but 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."