Sergio Perez warns against Force India team orders for 2018 F1 season

Perez and Ocon were under team orders not to fight each other for the rest of the 2017 campaign after they collided twice at the Belgian Grand Prix in August.

"We have got to understand how difficult it is going to be next year," Perez told Autosport.

"We'll have the Renaults and McLarens pushing us hard. So we need to push freely if we are to be in the fight.

"We also need to have a car that is competitive from the beginning, to be in the fight from the start and be in the fight for the season."

Perez said his relationship with Ocon had improved since they last collided at Spa and both know where they stand.

"We hit a very low point on our relationship in Belgium," he said. "But things have got a lot better since then.

"We're working professionally. We know we work for a team and we have to do the best for them, especially for next year.

"It's going to be a massive challenge, given the competition and threat from bigger teams which have struggled."

Perez finished seventh in the drivers' standings, just one place and 13 points clear of Ocon, whom he praised for the job he did in his first year with the team.

"Esteban came to F1 really well prepared with his experience in the previous categories and relationships with F1 teams," said Perez. "So that was good for us.

"Every driver's personality is different. Certainly Esteban is someone who can be quick.

"He understands what he needs and that is important. He's been on it this year."