Iran coach Branko Ivankovic has given his full backing to veteran striker Ali Daei ahead of Saturday's clash with Portugal, insisting he will keep the struggling forward in the line-up for the must-win match in Frankfurt.

The 37-year-old has come under scrutiny following a disappointing performance in the 3-1 opening loss to Mexico, with critics claiming he is a far cry away from the striker who has a record 109 international goals.

It was widely believed Ivankovic would drop his ageing star against Portugal - but the Croatian boss now sprung a surprise by doing just the opposite.

"There will be no line-up changes," Ivankovic said at a press conference in Frankfurt.

"Ali Daei is the leader in our team and very important. Without a leader, no team can make a good result."

Word out of the Iranian camp is that several team-mates have been at odds with Daei, especially after the striker cited a back injury for his poor showing against Mexico.

There was also a report about a verbal bust-up between Ali Karimi and Daei during half-time of the opener, but Ivankovic has dismissed the claims.

"It is not true," he stated. "Only I was talking (during the half), about the game."

While a win might not suffice to keep Iran in the tournament, charismatic Ivankovic has warned not to take the do-or-die encounter too seriously.

"This is sports, this is football and this is fun," he said.

"It is not death or life or to be or not to be. We will try to do or best."

Ivankovic hopes for his players to build on the performance from last Sunday against Mexico.

"The result does not always show a good picture," he said.

"But I am satisfied with how we played. We did a lot of good things. We created a lot of good opportunities."

He is confident "luck will be on our side" for the clash with Portugal.

"They have world-class individual players - that is the quality of Portugal," he said.

"But in the last 40 years they have not qualified for the second stage."

But he rates Luiz Felipe Scolari's players very highly.

"They are one of the favourites to win the World Cup. They came here with high ambitions but we have the right to hope we can make something happen.

"We have good players and good teamwork and hopefully better luck than against Mexico."

Ivankovic would not only speak about his line-up - which will remain unchanged - but also about Portugal's.

"I am sure (Cristiano) Ronaldo won't play," he said of the Manchester United star, who has repeatedly sat out training due to leg muscle problems.

And asked how he could be so sure, Ivankovic pointed to his nose and said: "I know."