The Brazilian football great meanwhile said he saw no problem with Diego Costa, Atletico Madrid's Brazilian-born striker, playing for Spain in next year's World Cup.

Ronaldo. Pic/ AFP

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"Players who are not used in their own country and have a second citizenship are used by other countries," he noted.

Costa recently indicated he would be keen to play for world champions Spain.

And Spain coach Vicente del Bosque said he was prepared to call on him if football's world governing body FIFA declares him eligible.

"If a player cannot play for his own country, why would he not be able to play for another country," said FIFA secretary-general Jerome Valcke.

Ronaldo played for Brazil in 98 international matches, scoring 62 goals and was part of the national squad that won the 1994 and 2002 World Cups.

The question of eligibility follows England midfielder Jack Wilshere's comments that only English players should represent the national side.

The Arsenal star was speaking after it emerged the Enlgish national governing Football Association had looked into the eligibility of talented Manchester United forward Adnan Januzaj to play for England.

Belgium-born winger Januzaj can play for the country of his birth, Albania, Kosovo, Serbia and Turkey and the 18-year-old could represent England in 2018 on residency grounds if he remains in the country for the next five years.