Fernando Alonso admits Suzuka has represented a "step backwards" for McLaren after he and Jenson Button were forced to settle for 15th and 17th on the grid.
Honda came to its home race hoping for a competitive weekend but dropped off the pace on Saturday. Alonso switched to Honda's upgrade in Malaysia so he could run it this weekend without a penalty but still faces a start towards the back end of the grid.
Alonso admits McLaren needs to hope for showers for Sunday's grand prix.
"Definitely not the right performance in qualifying," Alonso said. "All weekend long we have been struggling a little bit, trying to find the balance and speed of the car as well. Definitely difficult positions to start the race tomorrow, 15th and 17th are not the best places for the two McLarens, especially after some races we were used to being in Q3 and fighting for the points.
"So it seems to be a step backwards here, especially yesterday and Saturday, so we need to find some speed for tomorrow ... some weather change, some rain will help us recover some places. But we need to analyse why we underperformed."
Alonso thinks McLaren is still struggling to find the ideal set-up on both cars.
"So far it has been disappointing, no doubt. It's not great for our home grand prix but we didn't find the speed all weekend long, we're struggling with the high-speed performance and straight-line performance.
"Difficult to balance this in terms of downforce choices, etc, so not the ideal place to start the race but hopefully we can recover some places, maybe some rain around tomorrow because in a normal race, normal circumstances it will be difficult to gain places."
Though admitting it's been a step backwards, Alonso does not believe it is a sign McLaren and Honda's latest upgrades have gone in the wrong direction.
"I think everything is working. Five days ago we were performing really well in Malaysia. It's just circuit to circuit seems to change the performance of the car, or our competitors - here it seems Force India and Haas are running very quick, in Singapore Toro Rosso was running very quick. So depending circuit to circuit and this one is probably not in our sight, so we need to understand why."