Sebastian Vettel says he sees new Ferrari team-mate Charles Leclerc as a "full rival" this season.
Vettel, 31, has been the team's lead driver for four seasons while Leclerc, 21, has been promoted after one season with the affiliated Sauber team.
"He's got the seat for a reason. I've got to take him very seriously," said four-time world champion Vettel.
"You always have a close rivalry with your team-mate. He will be quick enough and put me under pressure.
"But priority one is to bring the team forward."
Vettel's remarks came at the end of the first day of pre-season testing, on which he was fastest, prompting Mercedes F1 boss Toto Wolff to say Ferrari looked "ultra-strong".
Vettel had an up-and-down season in 2018 - taking five wins but missing the chance to beat Mercedes driver Lewis Hamilton to the title by making a series of high-profile errors.
Last week, new Ferrari team principal Mattia Binotto said they could favour Vettel over Leclerc early in the season if the circumstances arose.
"It's normal, especially early in the season, that if there are particular situations our priority will be Sebastian," Binotto said.
"He is the guide with which we aim for the championship. But there's no prejudice - the absolute priority is for Ferrari to win."
Binotto said having such a competitive driver pairing was "not a problem but an opportunity".
"Sebastian has little to prove, and he remains our guide," he said. "Charles still has to learn, as pointed out by himself, but we know how talented he is.
"I hope to have this problem of having two drivers to manage among the top positions."
Binotto did not specify the circumstances in which Vettel might be given priority when the season starts in Australia next month.
Vettel said on Monday he was pleased with the new Ferrari on his first full day of testing.
"We couldn't have hoped for a better day," Vettel said. "It was unbelievable.
"The car was working really well. We had no issues slowing us down, we did the programme just the way we wanted, we were able to squeeze a little bit more out even.
"It's the first day, and it's meaningless in a couple of weeks, but for now, huge compliments to everyone in the factory, how they have tackled the new regulations and what they put on track is very close to perfection for the first day of driving."