Japan coach Takeshi Okada is unhappy that tactics honed in closed practice sessions have been leaked and could benefit the team's Group E opponents.

Okada urged his players to guard secret strategies in the wake of Japan's 1-0 loss to the Netherlands on Saturday.

He did not elaborate on the source of the leaks but indicated that players had been too forthcoming in their comments to Japanese journalists.

"Details of closed training have been revealed and I think that was unfortunate," the 53-year-old Okada said. "I would like to again caution the players on this point."

Okada said set-piece strategies are crucial to Japan's success in its last group match against Denmark.

"We are lacking that quick forward, but we never count on a single player. We score as a team," Okada said. "Goal scorers can be enabled in various ways. We have to stay strong in defense and midfield, and we have to connect the passes better in midfield."

After losing all four of its warmup matches, Japan won its World Cup opener 1-0 over the favoured Cameroon. Keisuke Honda provided Japan's only goal so far, chipping in a cross from Daisuke Matsui against Cameroon.

On Saturday, Okada made no changes to the starting lineup to take on the Dutch. He praised the role played by former Celtic set-piece specialist Shunsuke Nakamura, who was benched for the opening match but who came on for Matsui in the 64th minute on Saturday. It could signal a return to favor for the skillful midfielder who turns 32 next week.

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