Tsuboi and his teammate in the au-sponsored #36 TOM'S GR Supra, Giuliano Alesi, came to Sugo in need of a big result to keep the team's fading title defence hopes alive.
But after a strong run to fifth in practice, a turbo issue in qualifying prevented Tsuboi from setting a lap in Q1, condemning he and Alesi to a back-of-the-grid start.
