Grosjean managed to finish eighteenth in the overall standings, scoring only eight points out of 21 races this year.
Grosjean explained that the team had simply not done a good enough job in the development of Haas' 2019 chassis, the VF-19, but is sure it can be improved upon for next season.
"Yeah the car was not good enough and we all know that," Grosjean commented. "Saying that everybody worked as hard as they could and we done the best job possible.
"Here, we came with an update and unfortunately Valtteri ruined that on Friday night and it was not always going to be easy to change the car, hard to change the car."
Although he spoke of how he feels the team have plenty to improve upon, Grosjean also noted that there are many things he needs to improve upon personally.
Grosjean felt that his initial race starts was one of his main weaknesses over the course of the season, but just like the overall improvement in the team, Grosjean feels that this is also something he can quickly regain for next season.
"I need to improve myself and my starts, that's really been a weakness of mine," Grosjean added.
"Especially Kev was next to me it was P10 and the end of the first lap I was P17 I believe so yeah I need to work on that and maybe there is time there and we have got more chances to be in the points but yeah, not an amazing race.
"We drove the best as we could both drivers and just the car we have is the car we have. We are working hard and I think next year is a good surprise."
Bahrain International Circuit - Winter testing