Japan could be without the services of Hiroki Sakai for Sunday's World Cup clash with Costa Rica.
The 32-year-old was forced to miss Thursday's training session due to the injury that forced him off the field in Wednesday's shock 2-1 victory over Germany.
Takehiro Tomiyasu would be Sakai's natural replacement, although the Arsenal defender also missed training on Thursday, so he faces a battle to prove his fitness ahead of this contest.
Head coach Hajime Moriyasu is expected to keep faith with the majority of the side that started against Germany despite the impact that the substitutes had on the final score.
Wataru Endo and Ao Tanaka should again start in central midfield, with Maya Yoshida captaining the side from the middle of the defence.
Takuma Asano came off the bench to score the winner against Germany, and he could come into the starting side for this match, potentially taking the place of Daizen Maeda at the tip of the attack.
Yuto Nagatomo was also replaced in the second half against Germany, but it was a tactical decision from the head coach, so he is fit to start on Sunday.
Takumi Minamino also had an impact as a substitute in the team's first match in Group E, but the 27-year-old, who is the leading goalscorer in the squad with 17, is again expected to start on the bench.
Japan possible starting lineup: Gonda; Tomiyasu, Itakura, Yoshida, Nagatomo; Endo, Tanaka; Ito, Kamada, Kubo; Asano
> Click here to see how Costa Rica could line up for this contest
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