Valtteri Bottas says Mercedes cannot be considered the favourites for this weekend's returning French GP, admitting Ferrari's form means F1's world champions must improve all areas of their 2018 car.
Mercedes boss Toto Wolff described Sebastian Vettel's serene victory at the last race in Montreal as a "wake-up call" for his defending four-time champions, on a weekend they had to delay their planned engine upgrade.
The world champions are hopeful of introducing their second-generation 2018 engines at Paul Ricard but, while optimistic of improvement from the W09, Bottas says Mercedes have to raise their game.
"It's different grand prix, different kind of tyres and it's positive we're going to have the new engine, which we would have needed [in Canada] to win the race," said Bottas, who finished second to Vettel in Montreal.
"Hopefully we can have some other upgrades as well on the car because every team is developing now race by race and the competition is getting tougher.
"We came [to Canada] knowing that in theory it would be a good track for us. We came with even the old engine thinking there's a very good chance we were going to be fighting for the win. But it wasn't the case and it shows how tough the development race is now and we need to keep improving.
"We are definitely not the favourites for the French Grand Prix, that's a fact."
While missing out on the performance advantage a fresh power unit at the last race would undoubtedly have brought, Bottas says Mercedes have to look at all areas of their W09 car for improvement.
"We can't just blame the old engine, it's also the car," said the Finn.
"We need to improve the car. We have seen that on tracks with many corners like Monaco we were far away from being the best car. So we have work to do in all the areas, definitely."
Mercedes retain the lead of F1's Constructors' Championship after seven rounds, leading Ferrari by a reduced 17-point margin, but Vettel overtook Lewis Hamilton at the top of the Drivers' Championship at the last round and hosts a one-point lead.