"Of course Portugal are stronger than Morocco. But the game is not going to be easy. We must respect all our opponents. Any game at the tournament is difficult and I can't say that one match will be easier than the other. We need to study every opponent," said the AC Milan striker.

Iran currently sit top of Group B having beaten Morocco 1-0 in their opening fixture, while the favourites to progress, Portugal and Spain, played out a thriller of a 3-3 draw.

"Morocco lost their first game - now they will be giving their all. They are used to playing against European teams, many of their players play for European clubs. The game is going to be difficult but I hope we will manage to win," Silva said.

Reigning European champions Portugal will face Morocco at the 78,000-seater Luzhniki Stadium in Moscow on Wednesday after playing out a 3-3 draw with Spain in their first match on Friday.