• Source close to Real Madrid striker says he wants to leave Spain • Former United man said to be furious over tax allegations

Manchester United are watching the Cristiano Ronaldo show with renewed interest after the Real Madrid striker made it plain he is “outraged” at what he feels is unfair treatment by tax authorities and is now determined to leave Spain.

The 32-year-old feels he is being singled out for disproportionate treatment after prosecutors accused him of defrauding the authorities of €14.7m. A source close to the player claims the “outraged” Portugal international “feels great indignation” following the public speculation about his tax affairs and a sense of “injustice” at the allegations – which he contests – and he has made a decision to leave the country.

Ronaldo, who signed a new five-year contract in November, has made no secret of his affection for United – the club he left to join Madrid in 2009 after six years at Old Trafford – and José Mourinho, who shares the same super agent Jorge Mendes, would relish his return as he seeks to build a team capable of a title challenge and a successful campaign in the Champions League.

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United remain one of the clubs with the financial muscle to offer a competitive package for Ronaldo – they are predicting record revenues of up to £570m this year – and his return would be a dream commercial move.

He has a €1bn (£880m) release clause in his current Madrid deal and United – now without Zlatan Ibrahimovic’s wages on the books and the potential to lose Wayne Rooney’s financial burden soon – would be able to meet Ronaldo’s wage demands of around £400,000 a week. Paris Saint-Germain could match United’s offer but the Old Trafford move presents Ronaldo with his fairytale moment and a far grander stage on which to perform. The potential availability of one of the world’s most marketable players will also naturally alert the Chinese Super League clubs.

Reports that Ronaldo wanted to leave Real were sparked on Friday in the Portuguese newspaper A Bola. It claimed his decision was “irreversible” and that he has already told his Madrid team-mates that he wants to leave.

The root of Ronaldo’s anger stems from Spanish prosecutors’ lawsuit against the player, accusing him of defrauding tax authorities of €14.7m by hiding his image rights income between 2011 and 2014. Ronaldo has categorically denied any wrongdoing. Real backed that assertion, saying they were confident the Portuguese forward had acted legally.

Following the tax allegations, Ronaldo posted a picture of himself with his fingers to his lips on Instagram with the caption: “Sometimes the best answer it’s to be quiet.”

Earlier this week Ronaldo’s agency Gestifute released a statement which read: “There is no tax evasion scheme ... There has never been any hiding nor any intention to hide anything.”

Ronaldo’s frustrations at his treatment come after leading Real to three Champions League titles, scoring twice in last month’s final against Juventus in Cardiff as they became the first club to retain the trophy. He also became only the second player to score in three different finals and remains the competition’s record goalscorer with 105.

Barcelona’s Lionel Messi took a similar stance in threatening to quit Spain in 2014, also claiming he had been singled out for special treatment, when he was accused of concealing €4.1m from the authorities. The Argentina international was found guilty and subsequently lost an appeal against a 21-month prison sentence – under Spanish law sentences under two years are usually suspended – and a €2.1m (£1.8m) fine.