Romain Grosjean feels the gap between Haas and the leading three Formula 1 teams is bigger than anticipated at the start of the 2019 season, fearing the deficit will only grow as the year wears on.

Haas finished as the leading midfield team at the season-opening Australian Grand Prix as Kevin Magnussen crossed the line sixth, only trailing Mercedes, Red Bull and Ferrari at the front of the pack.

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The trio have dominated F1 for some time, taking every race win in the past six years, but there were hopes the gap to the midfield had shrunk following a tweak in the aerodynamic regulations for 2019.

Looking ahead to next weekend's Bahrain Grand Prix, Haas driver Grosjean said that while the close-knit midfield battle was good for F1, the gap to the leading teams remained large.

"I think it’s the right battle for Formula 1. It’s super exciting to look at the midfield, where the gap is very tight and you never know who’s going to end up on top," Grosjean said.

"I think we’re a bit further away from Red Bull than we were hoping. I’m afraid the gap could open during the year because of the resources they have.

"We’ll definitely try to give them as hard a time as we can, to please both Rich Energy and ourselves." (Haas' title sponsor, Rich Energy, has been very open about its ambitions to challenge fellow energy drink company Red Bull both on- and off-track.)

Grosjean's thoughts were echoed by teammate Magnussen, who said he expected Red Bull in particular to make big strides across the course of the year.

"It’s still going to be very difficult to reach Red Bull as they’re already quite a big chunk ahead of us," Magnussen said.

"They usually evolve and develop quite well over the season, even compared to the two other top teams of Mercedes and Ferrari."