Japan Football Association (JFA) President Motoaki Inukai said the Blue Samurai needed toughening up before the finals in South Africa, which begin on June 11.
"It's the first time in a long time Japan will play South Korea with both teams fielding their best line-ups," Inukai told Reuters before Japan's World Cup send-off at Saitama.
"It is risky, but if you don't take those risks with less than a month to go they don't (get) that sense of what the World Cup is all about."
Japan coach Takeshi Okada has chosen three tough opponents in the run-in to the tournament with fixtures against England and Ivory Coast after their South Korean test.
South Korea have notched 33 wins to Japan's 10 in their previous 61 meetings and their last victory at the East Asian championship earlier this year almost cost Okada his job.
Inukai refused to shake Okada's hand after Japan were overpowered 3-1 in Tokyo but insisted he was squarely behind the coach.
"I don't get too nervous about friendly results," said Inukai. "The coach wants to play the top teams and feels that if we lose then tough luck.
"Before the 2006 World Cup we won lots of games and the Japanese media were jumping up and down and saying we could get to the semi-finals or even further -- and look what happened."
DEEP SCARS
Japan's meek early exit from Germany four years ago under Brazilian Zico left deep scars, and on paper it looks like they will struggle to make it past the first round in South Africa.
Okada's side face Cameroon, Netherlands and Denmark in Group E. Victory against 2002 World Cup semi-finalists South Korea in Saitama would give them an enormous confidence boost.
"What I want from Japan is to go out and try to win every match," said Inukai, who will be looking for a new coach at the end of the World Cup with Okada's bags already packed.
Inukai would not reveal the identity of any potential JFA targets but flatly denied former German World Cup winner Guido Buchwald was poised to take over.
"I don't know where those reports came from," he laughed.
"It's not quite as bad as the English media but there is no basis whatsoever in those reports. It certainly won't be Guido!"
Ikunai also had a dig at Okada for likening the Japan side to a "swarm of feasting flies" at his squad announcement.
"The world 'flies' wasn't good," he said. "I wish he'd said 'wasps' at least. We want them to go there and sting."
