Right winger Akira Kaji is Japan's only major injury worry ahead of their World Cup opener against Australia in Kaiserslautern on June 12.
Alex, Atsushi Yanagisawa and Naohiro Takahara have all made progress in their recoveries from minor fitness problems, but Kaji's ankle complaint is still causing concern.
The Gamba Osaka defender suffered the injury during last week's friendly against Germany and coach Zico fears it will prevent him playing in a game Japan must win if they are to retain realistic hopes of progressing from Group F.
"I'm not too concerned about Yanagisawa or Alex," said Zico.
"The player I am most worried about is Kaji. He says his foot still hurts but we won't know exactly where he stands until after the next medical."