Iran would not have expected to reach the final round group games with a chances of making it through to the knockout stages.
Carlos Queiroz's side have shown themselves to be extremely tough competitors and they face the European champions with both teams knowing a win would put them into the last 16.
Iran continue to be without central defender Rouzbeh Cheshmi, who picked up a muscle injury in training last week that is set to sideline him for a month.
Cristiano Ronaldo is likely to lead the Portuguese attack once more, with the Real Madrid forward having scored in both of his country's previous games.
Iran's ultra defensive showing against Spain gave us an idea of how they are capable of playing, although in the final stretch of the game they opened up and created chances.
Expect the plan for Queiroz's men to be similar; keep things as tight as possible until the final 15 minutes or so then pour forward looking for a result.
Portugal themselves were extremely underwhelming against Morocco despite winning 1-0, and they could struggle to break down this resolute Iranian unit.
Tips and predictions
Portugal may have scored in the first half of both of their previous matches, yet Iran have kept clean sheet in the opening 45 minutes of their two group games.
Portugal themselves do not need to go crazy looking for a goal, while Iran are likely to play effectively with a six-man defence as they did against Spain - which should lead to a tight opening half.