“We know we are not the favorites, we have to be realistic, but in football nothing is impossible... The first match [against Spain], the group stage will be extremely difficult but… I am confident that we will give our best," Ronaldo said as quoted by the news website goal.com.

Ronaldo, Portugal's most capped player and all-time leading scorer, added that his team would be hoping to repeat the form that saw them win UEFA Euro 2016 .

"We will give our best and wait to see what we will get from it,” Ronaldo said.

Ronaldo has scored 81 goals in 149 matches for Portugal.

Russia’s first-ever FIFA World Cup will take place from June 14 to July 15 in 11 host cities. Portugal will face 2010 World Cup winners Spain as well as Morocco and Iran in Group B.