Mercedes have revealed the most striking car upgrade among their top team rivals in Barcelona.

Before the Spanish Grand Prix weekend, all the talk was of Red Bull and their plans for a supposed 'B' car after an uncompetitive start to 2017, but then the RB13 was seen in the Barcelona pits looking conspicuously similar to the one that raced in Russia.

"I don't want to underestimate Red Bull, but it will probably take some time before they can catch up to us," said Mercedes's Valtteri Bottas in Spain.

Red Bull's Daniel Ricciardo agrees: "Hopefully we will be closer, but we cannot expect to go out there and win. The gap was too big for that.

"Even if the upgrade gives us a second, Mercedes and Ferrari have not sat around doing nothing.

"It's still the same car. We've changed a lot of things but don't expect too much."

Indeed, more visually impressive is the upgrade brought to Barcelona by Mercedes, featuring a radically thinner nose that had to undergo new crash testing.

However, most experts doubt the car upgrades will significantly shake up the 2017 hierarchy.

"It's not a new season that's starting here," Haas driver Romain Grosjean told France's RMC.

"Mercedes and Ferrari are still going to be at the front, and we'll have to see how much closer Red Bull can get."

Mercedes lead Ferrari by one point heading into the Barcelona race.