Captain Kazuki Himeno failed to shake off a calf injury and was replaced by Amanaki Saumaki just before kick off of Japan's World Cup opener against Chile on Sunday.
It provoked a shuffle in the pack with Jack Cornelsen moving from the second row to take Himeno's spot at No 8 for the Group D game in Toulouse.
Saumaki, who was not in the original matchday 23, came in to fill the gap at lock with scrum-half Yutaka Nagare named as captain.
Himeno had missed the 'captain's run', the traditional eve-of-match training session, at Toulouse Stadium on Saturday.
"He has got a bit of a calf problem," assistant coach Tony Brown had said.
Ahead of the game Chile's defensive coach Emiliano Caffera identified the 29-year-old Himeno as one of the "key players" for Japan that needed to be stopped.
Teams (15-1)
Chile
Inaki Ayarza; Santiago Videla, Domingo Saavedra, Matias Garafulic, Franco Velarde; Rodrigo Fernandez, Marcelo Torrealba; Alfonso Escobar, Raimundo Martinez, Martin Sigren (capt); Javier Eissmann, Clemente Saavedra; Matias Dittus, Diego Escobar, Javier Carrasco
Replacements: Augusto Bohme, Salvador Lues, Inaki Gurruchaga, Pablo Huete, Santiago Pedrero, Ignacio Silva, Lukas Carvallo, Jose Ignacio Larenas
Coach: Pablo Lemoine (URU)
Japan
Semisi Masirewa; Kotaro Matsushima, Dylan Riley, Ryoto Nakamura, Jone Naikabula; Rikiya Matsuda, Yutaka Nagare (capt); Jack Cornelsen, Kanji Shimokawa, Michael Leitch; Amato Fakatava; Amanaki Saumaki, Jiwon Gu, Atsushi Sakate, Keita Inagaki
Replacements: Shota Horie, Craig Millar, Asaeli Ai Valu, Warner Dearns, Shota Fukui, Naoto Saito, Tomoki Osada, Lomano Lemeki
Coach: Jamie Joseph (NZL)
Referee: Nic Berry (AUS)