The Portugal international has spoke about his discontent at Real Madrid following their Champions League triumph last month.
Ronaldo was quick to speak out in the media about his unhappiness at The Bernabeu despite winning a fourth European crown at los Blancos.
Some reports suggest that Ronaldo is happy that FC Barcelona star Lionel Messi and Paris Saint-Germain forward is paid more than the Portuguese star.
The 33-year-old moved to Real Madrid in an £80m deal from Manchester United in the 2009 summer transfer window.
Ronaldo won three Premier League titles, the Champions League, the FA Cup and two League Cup triumphs.
Sunday Times reporter Castles doesn’t expect Ronaldo to return to Manchester United in the summer transfer window.
“Man United aren’t a strong possibility,” Castles told the Transfer Window podcast.
“They are more likely to recruit on the right hand side of the attack and working on a deal for Bale.”
Ronaldo has scored an incredible 450 goals in 438 games during nine seasons at Real Madrid.
Manchester United finished in second place in the Premier League table last term to secure Champions League football.
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