Yusuke Hasegawa had admitted that the cancellation of Honda's engine deal with Sauber is a major blow to the Japanese manufacturer.
The partnership was announced in April at the Russian Grand Prix. However the departure of team principal Monisha Kaltenborn in June heralded a change in strategy for the Swiss team.
The arrangement was cancelled at the end of July by new team boss Frederic Vasseur. Sauber has now signed a new engine contract with Ferrari instead.
Hasegawa, Honda's head of F1 project, agreed that this had indeed been very disappointing to the manufacturer, which is also currently struggling to hold on to its existing deal with McLaren.
"Of course it is very disappointing," Hasegawa told RACER magazine this week.
"It is a customer team program so it doesn't hurt our program very much," he added. "But we still expected to get the opportunity to get our engine running more.
"We would have got more data and been able to make comparisons, so it is very disappointing.
"More than that, on the practical side, we had to stop the preparation," he pointed out. "So it is very bad."
Negotiations with Sauber were conducted by Honda's motorsport manager Masashi Yamamoto. Hasegawa said he had little advance warning that the deal had fallen through, despite close links with Sauber technical director Jorg Zander.
"I wasn't in the meetings, that was Yamamoto-san," he said. "Zander and I were in very good communication all the time. We both didn't believe that we would have to stop this collaboration until the final moment."
For his part, Vasseur said that "the situation changed drastically on both sides" over the course of the eight months of discussions.
"We reached a point that at one stage it was better for everybody to stop the discussions," Vasseur concluded.
"We did it in a very fair way with Honda," he added. "I would like to thank them for the discussion we had.
"It's also a tricky situation for us.
"We are in a quite tough situation in terms of pace," he explained. "We need to have reference. On the Honda side, we don't know exactly what will happen with the McLaren deal."