After finishing fifth overall in 2018, the small and now five-year-old American team only managed to beat Williams in 2019.
"We blamed the tyres a lot at the start of the year," Grosjean told the French source f1only.fr, "but unfortunately it was wasn't only the tyres.
"It was really the car which had fundamental faults. Actually I think our understanding of the tyres is good. We used them as well as we could.
"It was just our car which was not good."
Therefore, there is a lot riding on Haas' comeback in 2020. BT newspaper claims the new car will only be launched on the morning of the first winter test on February 19.
But it has emerged that Haas' 2020 car has already passed the mandatory FIA crash tests, after recent sessions at the CSI facility in Bollate, near Milan.
"We are on schedule for the first winter tests in Barcelona," Grosjean confirms.
"Like every year, we will push the limits to the maximum, but for the moment we have no particular worries.
"I am excited to discover the new car. I think we will do the seat fit very quickly, so that will allow me to see the chassis, and then I will spend some time at the factory in England," the Frenchman added.
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