Magnussen qualified only 19th at Monza and was one of only three drivers to take a gamble by starting on the hard rather than medium Pirelli tyres.
However, while Lewis Hamilton and Valtteri Bottas used the strategy to have strong races and earn points, Magnussen finished 18th and last, behind team-mate Nico Hulkenberg.
The intention had been to run a long opening stint on the hard, potentially not stopping until the closing laps.
However, a lack of overall grip meant that Magnussen pitted as early as lap 12, obliging him to switch to two stops and effectively ruining his race.
"It should have been possible, but we just had no grip at all," he said when asked by Motorsport.com about the tyre gamble.
"And the car was so over-balanced, there was no chance. I mean, we couldn't even take off enough front wing. The flap couldn't go down low enough. And horrendous, really bad.
"I mean, we were talking about going all the way to the end on that first hard to then maybe hope for a late safety car, or do a bit like [Alex] Albon did in Melbourne, try something like that. But no chance whatsoever."
Magnussen accepts that he has to wait for improvements to make their way to the track.
"The work is being done in the background, and we just have to be patient on it until we can bring those parts to the car," he said.
"At the end of the day, we got a job to do, and we need to crack on until we until we get those parts, and we can't cry about what we've got at the moment, we've just got to work with what we have and always try and get something out of it, no matter how difficult it looks."
The Dane believes that the Haas organisation itself is in the best shape in its history.
"I still believe that the team is in a stronger place than it has been," he said. "It's just a paradox that we have probably one of the weakest cars we've had.
"With the strong foundation that I see in the team, I think we can do a lot better, and I think we will do a lot better.
"So it really is a patience game. It's about really sticking it out with what we have at the moment, and waiting for better things."
Asked what his own contribution would be, he said: "I think it's important to be there to support and give all the feedback that is needed. And at the same time just good faith, and give them peace to go and work on their stuff."
