Romain Grosjean has warned Renault it should be “scared” of Haas in the future in light of the teams’ year-long duel last season.

The American outfit ended the 2018 campaign 29 points adrift of Renault in the battle for fourth-place in the constructors’ championship but could have leapfrogged its rivals without a series of on-track incidents that lost crucial points.

Haas, who joined the Formula 1 grid in 2016, finished eighth in its first two years in the sport before jumping to fifth last year.

As it targets further improvement this season, Grosjean pinpointed where he felt the team could improve to overhaul Renault in 2019.

“There are few things. One example is that we don’t produce parts, so we need to manufacture them outside and sometimes it takes a bit too long,” Grosjean said, as quoted by Motorsport.com.

“That is one example that I can give out of few, but that is one. When it would take three days [for them], to our team to do it it maybe takes three weeks.

“Like the floor, we didn’t have the time to change it for Monza, that was the only thing. The performance gain is zero. Absolutely zero, zero, but we just didn’t have the time to do it for Monza and Renault played on it.

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“Gunther [Steiner, team principal] is well aware. You know, he understands a lot of things and that is great to have,” he said. “We talk very often, but he is aware of the things that we need to improve and definitely it is something that we’re working on.

“Part of the rest is just a growing process, more performance you want, faster you want to be, better things to go.”

Haas and Renault not only fought each other on track but were also embroiled in a battle off it when the latter launched a protest against Grosjean’s car at the Italian Grand Prix, resulting in a disqualification and a result that proved vital in the pair’s season-long duel.

Although this dealt a blow in Haas’ season, Grosjean reckons it was proof that Renault were wary of the threat it was posing.

“I don’t think it is a great sportsmanship move,” he said on Renault’s protest. “But yes, we were scaring them, which is good. They should be for the future.”