"Singapore is now behind us, but Suzuka will surely be a challenge," said the two-time former world champion.
"Our pace was more encouraging in Singapore, but I think it will be harder for us at Suzuka due to the characteristics of the track."
Having to be so downbeat about the team's prospects at Suzuka clearly pained the Spanish racer, who regards his visit to Japan as one of the highlights of the season.
"I’m full of anticipation about going to Suzuka," he said. "Like Jenson, I have a strong affinity with Japan, I love the country and I’ve always been fascinated by its culture.
"I’ve also loved racing there and I’ve won both at Suzuka and Fuji, so it holds a lot of special memories for me.
"The fans are one-of-a-kind and the circuit absolutely deserves its legendary status - it’s one of the most exciting on the calendar."
Unfortunately, that track is unlikely to suit the current McLaren - not that many circuits have seemed to suited it, if truth been told, as the team struggles through a deeply disappointing and frustrating year in their first year back in partnership with Honda.
"Our car is well balanced and feels good to drive, but on a circuit with such a high average speed it will be difficult to beat our competitors.
"It’s a really tough circuit, and a huge test for the drivers, as a lot of it is really narrow and bumpy so you need absolute commitment into every corner.
"It has almost the opposite characteristics to Singapore in terms of set-up, so it’s a very different challenge."
Regardless of the difficulties in store for the team again this weekend, Alonso promised to pull out all the stops and try to deliver something special for the fans.
"Of course we’ll do everything we can to maximise our performance at what is a fantastic racetrack and Honda’s home Grand Prix.
"We’ll take the samurai spirit with us to Suzuka, and as usual we won’t give up," he promised.