Mick Schumacher and Nikita Mazepin both set out on their rookie Formula 1 campaigns this year after making the step up from Formula 2, Schumacher graduating as the series champion.
However, Haas struggled last year, finishing ahead of only Williams, and team principal Guenther Steiner has made clear there will be no developments being made to the car across the year.
Despite lacking pace, Magnussen said the Haas VF-20 will give both rookies a good feeling.
“I don’t think they are going to find a difficult car to drive," said the Dane, now racing in the IMSA sports car series.
"As we have seen, these cars are very good and many times I’ve driven the car and thought ‘this has got to be competitive’ because the feeling has been pretty good, but it just isn’t and we’re slow because we lack a bit of everything, quite a bit of everything.
“That’s really what makes us uncompetitive, but not really because the car is particularly difficult to drive. I think they are going to find it very fast and enjoyable to drive.”
Grosjean, who had been a raced for the team in each of its previous five seasons in the sport, added he believes the Pirelli tyres will present the biggest problems for Schumacher and Mazepin.
The Frenchman added: “I think generally Formula 1 is difficult for a rookie but the car is, it’s a bit understeery, so in that aspect, it’s not too hard to drive.
“I guess it’s always going to be a key of getting the tyre to work and with the 2021 tyres we don’t know how it is going to go.
GPFans is a multi-platform, multi-language brand dedicated to Formula One coverage. We bring you all the ins and outs of the sport, 24/7, everything from up-to-the-minute news and features to the latest viral stories and clips.
We believe that a new generation of exciting, outspoken drivers will make F1 more popular than ever before, and we want to give our users access to as much of their heroes as possible, on and off the track. From Lewis Hamilton to Max Verstappen, Daniel Ricciardo to Sebastian Vettel, we provide in-depth analysis of every every Grand Prix in the season, from Australia to Abu Dhabi.
With Formula One under the new ownership of Liberty Media, how the sport is being covered is evolving, and GPFans will look to be at the heart of this progression into new media, as one of the fastest-growing sites covering the king of motorsports.