Spain's desire to call up Barcelona teenager Ansu Fati for next month's Under-17 World Cup has not gone down well with the Catalan club, sources have told ESPN FC.

Ansu, 16, has been one of the stars of Barca's season so far. He became their youngest ever goalscorer in La Liga last month against Osasuna and the youngest ever player to debut in the Champions League for the club against Borussia Dortmund this week.

However, the Spanish champions could be without Ansu for up to five weeks if, as expected, he is included in Spain's squad for the upcoming World Cup, which starts on Oct. 26 and runs until Nov. 17.

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Sources at the club have told ESPN FC they feel it will be detrimental to take Ansu out of the first-team dynamic and they fear losing him for so long would halt the progression he's made this season.

Barca coach Ernesto Valverde wants the player, who began preseason with Victor Valdes' U19 team, to train with the first team for the whole season, although there could still be times when he plays for the B team in the Spanish third division.

Ansu was born in Guinea-Bissau but moved to Seville when he was six. He has never represented any country at youth level and, until now, no one at the Royal Spanish Football Federation [RFEF] had moved to ensure his international future would be linked to Spain.

Steps have now been taken to nationalise him, though, following his brilliant start to the campaign. A RFEF spokesman confirmed to ESPN FC earlier this week that they are pursuing the necessary paperwork for him to obtain a Spanish passport.

Spain U17 coach David Gordo also revealed that he hopes to have Ansu available for the World Cup, and that the forward was keen to represent La Roja. The 16-year-old is also eligible for Portugal and Guinea-Bissau.

Spain's first game at the tournament is against Argentina on Oct. 28, but there will also be travelling and training time before then. If Spain progress in the competition, Ansu would be away from Barcelona until towards the end of November.

Sources at Barcelona say that "removing him from the first team for that amount of time could be prejudicial," pointing out that Ansu could miss as many as seven Barcelona first-team games if Spain progress.

Ansu made his debut for Barca against Real Betis off the bench in August and scored against Osasuna as a substitute the following week. He made his first start against Valencia last weekend, scoring and assisting, before playing an hour in Tuesday's goalless draw at Borussia Dortmund in the Champions League.