Japan midfielder Hotaru Yamaguchi remains doubtful and could force coach Vahid Halilhodzic into further tinkering for the World Cup qualifier against Iraq on Tuesday, when a win would massively boost the chance of finals appearance in a year's time in Russia.

"This is the most important game. We need valiant players with real strong determination," Halilhodzic told a press conference on Monday, aware that a win will lift Japan three points above rivals Saudi Arabia and Australia with two games to go in Group B.

But he might not be able to call upon lynchpin Yamaguchi, who scored the last-gasp winner against Iraq when Japan scraped out all three points with a 2-1 home win in October.

Having suffered a lower right leg injury on Wednesday in a 1-1 warm-up draw at home to Syria, Yamaguchi continued to train apart from the team on Sunday in the Iranian capital in searing heat topping 35 C.

With Shinji Kagawa already out after he dislocated a shoulder 10 minutes into the Syria game, Yamaguchi's potential absence could see the Franco-Bosnian vastly realigning his starting midfield. Gamba Osaka's Yosuke Ideguchi replaced Yamaguchi to make his national team debut against Syria and could retain the sole holding midfield position.

"Hotaru isn't training fully, hence we don't know if he can play (in the Iraq game) straight in," said Halilhodzic. "It's a difficult situation, especially the midfield."

"We are without (long-term absentee and captain Makoto) Hasebe and Kagawa. We aren't sure on Hotaru and (Yasuyuki) Konno. (Hiroshi) Kiyotake isn't here either. But we have to do it despite saying all that. I'm telling the players we'll win this."

Genki Haraguchi played on the left wing against Syria but could drop into an attacking midfield role, while Keisuke Honda, who replaced Yuya Kubo as a right wing at the break in that game, could retain the other attacking midfield slot he finished the game with.

"We've tried many things with Honda, which was to find a solution. We'll make decisions after looking at things during training," the coach said.

If a make-shift setup is one thing Halilhodzic is having to contend with, a 4:55 p.m. start at PAS Tehran Stadium won't be doing him or his team any favor either with the venue's facility issues ruling out an evening kick-off.

"I think matches won't be held normally in heat like this...there's a health risk," Halilhodzic said. "We have to start hydrating not on the day of the game, but a day before, all organs inside the body need to adjust. It's high in altitude too here, it was hard even to breathe at the start."

Iraq, ranked 120th in the world, are already out of the qualifying race but Halilhodzic knows full well the likes of Udinese's Ali Adnan has what it takes to derail his team.

"Ninety percent of their players experienced the Rio Olympics, according to my analysis. They have wonderful qualities," he said. "They are strong physically and mentally. They had a managerial change too and I think their motivation is higher after that."

A defeat in Tehran would leave Japan level on points with Australia, who Japan host on Aug. 31, and Saudi Arabia, where the Blue Samurai have to visit on Sept. 5 in the final fixture.