Fitness concerns over Hawar Mulla Mohammed and Saleh Sadir, plus the suspension of Qusay Muneer, has left the Brazilian needing to reconsider his starting line-up for the match with the co-hosts at Bangkok's Rajamangala Stadium.

But for Vieira, who only took over as Iraq coach in May, those changes are nothing new.

"I have played 11 games and I can honestly say I have not started the same team in each match," said the Brazilian.

"And in match number 12 the team will be different again."

Hawar injured his Achilles tendon in the goalless draw against Oman while Saleh appeared to suffer a re-occurrence of a knee injury in the 3-1 win over Australia.

Even without the midfield trio many consider Iraq favourites to advance to the final four, although Vieira was keen to play down the tag and warned against any complacency.

"We have to respect Vietnam because to get to this stage then they have had to qualify on merit," he said

"Don't forget they beat UAE, who won the Gulf Cup a few months earlier, and they got a good result against Qatar. Okay they lost heavily against Japan but we cannot analyse them on this one match.

"Our players are not over confident at all. I pressure the players not to think that way. If you remember many people said that we were the underdogs in our match with Australia."

Vieira's counterpart, Alfred Riedl accepts that Iraq are the favourites to go through and the Austrian, who will be without influential playmaker Phan Van Tai Em on account that he is getting married, has called for his team to show their mettle.

"We are underdogs and they are the favourites," said Riedl, who is currently in his third stint as Vietnam head coach.

"We need to have the fighting spirit we showed in the first two matches. The third match did not help us because Japan were simply too strong for us.

"I can't say there are any weak points in Iraq and we have to deal with this. The players have got to go out and show their strength tomorrow. We don't need small boys we need men.

"The Iraqis are very strong physically and this might make the difference. But we will do everything we can to win this match as it is a decisive match as there can be no draw."