The team-mates qualified well for the British Grand Prix but lost positions when they collided while fighting for position on the opening lap.
While Grosjean escaped without damage, Magnussen’s car took a hit and he limped home in ninth place.
“In Silverstone we qualified again seventh and eighth, we were in a fantastic position to score points with two cars,” team boss Guenther Steiner told the official F1 website. “We ended up scoring barely with one car.”
Asked what he told his drivers, the Haas boss replied: “What happened afterwards? I don’t want to explain that… Not a lot.
“We just came to a conclusion that this cannot happen again. We cannot throw away points at Turn 1 when we are not in danger of being overtaken after the start. That was the outcome.
“We just need to not throw any more points away. It’s so difficult at the start to make rules of engagement. The only rule of engagement is don’t do anything stupid. Do nothing that will compromise the team.
“We need to work for the team and make as many points as possible going forward. We’ve lost way too many.”