Honda's Formula 1 chief says more time is needed before anyone can properly judge just how much progress his company has made with its upgraded engine.
The Japanese manufacturer had gone into the Belgian Grand Prix hopeful that improvements to the combustion of its engine would deliver a positive step forward.
But the nature of the track made it hard to judge the scale of progress, which is why he thinks it may take a few more races to find out just where Honda compares now to the other manufacturers.
Yasuhisa Arai said: "We planned the update before the summer shut-down. It was on schedule and we confirmed it on track and also dyno.
"Unfortunately it did not work effectively [at Spa] because it is a very tough circuit, and also we lost time to run on day one and day two.
"So we cannot confirm in detail [the improvements]. We need more time."
Project not mature enough
McLaren and Honda had clearly hoped for better progress than they have made so far this season, with it unlikely it is going to achieve its pre-reason target of podiums or race wins.
Reflecting on what has gone wrong, McLaren racing director Eric Boullier said that Honda had perhaps started much further behind than predicted.
"We are happy to have Honda as a partner and Honda is happy I guess with McLaren so far," he said.
"It is just a project that maybe didn't have the maturity enough to be performing as much as we were expecting.
"But clearly we are working very hard as a works team and it is very, very important for us to be a works team."
Alonso keeps faith
But he continues to believe that things can turn around soon.
"There are some difficulties that we are going through now, but we are going through them together," he said.
"We have the right experience from all the parts to make this as short as possible hopefully, and I am happy with the progress.
"The starting point was maybe too low and not mature enough, but we are getting there. Unfortunately Spa and probably Monza will not show much of the progress we saw in Hungary where we were more or less top ten in all the sessions.
"Hopefully we can see something similar in Singapore or the next races. For future races or next year things will look completely different."