Japan coach Zico has warned his players to be aware of the threat posed by Harry Kewell in Monday's World Cup clash against Australia.

The Liverpool winger has been struggling with a groin injury for the past few weeks, but Zico knows even a 50 per cent fit Kewell is capable of putting a major dent in Japan's hopes of progressing from Group F.

The Blue Samurai boss said: "Even if Kewell comes off the bench we know he has the ability to make an immediate impact. We will have to keep him firmly in check."

With Croatia and Brazil still to come, Japan cannot afford to lose against the Socceroos in Kaiserslautern if they are to retain realistic hopes of reaching the last 16.

"I'm confident we can come away with the result we want," added Zico.

"We have been working towards this point for four years and want to get off to a strong start.

"Australia are a tough side. We know that. They have many experienced players but so do we. We should be able to take three points if we play our game."