Mercedes driver Valtteri Bottas admits Ferrari are further ahead than expected after an impressive few days at pre-season testing in Barcelona.

The Silver Arrows are once again heavily fancied to win the Constructors’ Championship in 2019, but early signs suggest they could face a more serious test from Ferrari, who are priced at 2.80 to win the Constructors’ Championship.

The new season began in earnest on Monday with testing at the Circuit de Barcelona-Catalunya although Williams had to delay their appearance.

Renault’s Nico Hulkenberg posted the fastest time on the final day in Spain, with team-mate Daniel Ricciardo third.

Toro Rosso’s British-born Thai rookie Alexander Albon split the Renault pair, with Bottas ending the day in fourth. Success in pre-season testing doesn’t guarantee the same results once the action officially begins, but Bottas is already keeping a close eye on their Italian rivals.

Bottas said: “They (Ferrari) do seem very strong. No matter which fuel loads or engine modes they’re running, they are quick.

“It appears they have a better package than last year, which means it will be a bigger challenge for us. I think we feel at this point they’re going to be a bit ahead.”

Ferrari new-boy Charles Leclerc isn’t getting carried away with their performance and insists other teams may be “sandbagging” – hiding their true pace.

Leclerc said: “The performance has no sense for now because it remains testing. They are probably not pushing and we are not either. We don’t know how much the others are sandbagging, so we’ll see at the first race.”