Barcelona - Sebastian Vettel said on Tuesday that he considers new Ferrari team-mate Charles Leclerc a "full rival" as the German prepares for his latest tilt at a fifth Formula One world title.
Monegasque Leclerc was the quickest driver on the second day of pre-season testing in Barcelona, clocking within 0.1 seconds of Vettel's leading time 24 hours earlier.
Vettel is heading into his fifth season with Ferrari since leaving Red Bull in 2014, having finished second to Lewis Hamilton in each of the last two years.
The 21-year-old Leclerc replaced Kimi Raikkonen at the Italian manufacturer after an impressive 10 points finishes in his rookie season with Sauber.
"Of course (Leclerc is) a full rival," said Vettel. "I think he is in the seat for a reason and I have to take it very seriously.
"But I think you always have close rivalry with your team-mate and priority number one is for sure trying to bring the team forward.
"I have been around for a bit longer compared to him, so it is different things maybe that he will have on his plate in the beginning... I am very certain he will be quick enough and put me under pressure so we'll see how it goes."
Vettel made a strong start to his 2018 campaign, before a series of individual and team errors saw him lose the race with Mercedes' Hamilton to become a five-time world champion by 88 points.
But he remains confident that Ferrari can clinch their first drivers' crown since Raikkonen's dramatic triumph in 2007.
"Obviously we've had better years and years we were further away," said the 31-year-old Vettel, who won four successive world championships at Red Bull from 2010-2013.
"But overall though the progression is there, the team is developing.
"So I hope that this year we get to have a lot of fun. Fun is to win a lot of races and then ultimately you are fighting for the championship.
"That's obviously what we want but at this point it is very far away."
The 2019 Formula One season gets underway with the Australian Grand Prix at Melbourne on March 17.