FC Barcelona legend Andres Iniesta has warned his Spain teammates about the danger Cristiano Ronaldo poses ahead of their 2018 FIFA World Cup clash with Portugal this week.

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La Furia Roja will play their first 2018 World Cup match against 2016 European Championship winners Portugal on Friday, one of the biggest matches of the first round of fixtures.

Iniesta has urged his colleagues to guard against complacency, though, and also feels Spain will need to keep a close eye on Ronaldo.

"Portugal is a team that takes a lot to defeat and we will have to perform at the highest level. In a World Cup, any small thing can knock you out," the legendary midfielder told Cadena Cope.

"Cristiano is a fundamental player for any team he is in, and for Portugal as well."

The 34-year-old, who left Barca to join Vissel Kobe last month, has also hinted at the possibility of hanging up his Spain boots after the World Cup.

"I will never close 100% the door of the national team after the World Cup, but everything indicates that this will be the case," he added.

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Ronaldo has scored 81 goals and assisted a further 36 strikes in 150 games for Portugal so far.

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