Ronaldo during his Manchester United days
Ronaldo played for seven seasons at Manchester United before joining Real Madrid

Manchester United legend Cristiano Ronaldo is once again being linked with a sensational return to Old Trafford following the former World and European player of the year's lack of a goal celebration during Real Madrid's 5-1 win over Granada on Sunday.

Last month, the Real Madrid icon was subjected to jeers from the notoriously fickle Bernabeu crowd during their defeat to Barcelona, when the former Manchester United star missed a spate of gilt-edged chances to cement their ultimately token lead.

The Portuguese international's record this season is the envy of Europe, with 21 league goals in 26 games, and yet the former Manchester United darling remains bizarrely unloved by a section of his club's support.

Ronaldo left Manchester United in the summer of 2009 and has since been regularly associated with an unlikely return to Sir Alex Ferguson's side. Recent income tax laws in Spain, whereby foreign players must now pay 54 percent since the abolishment of the 'Beckham Law', has heightened rumours suggesting Ronaldo could endeavour to return to Old Trafford.

When David Beckham left Manchester United in 2003, elite foreign workers were only required to pay 24 percent tax, but the abolishment of that rule, which was named after the Old Trafford icon, has certainly made it a more equal playing field.

According to The Sun newspaper, the precarious new financial rules, which would have a serious impact on Ronaldo's reputed £250,000 a week wages, in addition to the winger's well-documented fragile relationship with supporters, has led to both Manchester United and their bitter Premier League rivals Manchester City being linked as possible suitors.

While Ronaldo has regularly championed his love of life in Spain, recent developments on and off the pitch suggests all is not well with the Portuguese ace, who still enjoys a superb relationship with Manchester United's Sir Alex Ferguson.

The Sun intimate Real Madrid fans are growing weary of their side's inability to pip Barcelona to the top honours and while Ronaldo has been sensational for Los Blancos since leaving Manchester United in a world record £80 million deal, the 26-year-old has been held particularly culpable.

The aforementioned Manchester United manager would inevitably jump at the chance to re-sign one of the finest players in club's history. A move on that scale would not only silence the Manchester club's many detractors of late, but it would also be a huge PR coup for the United's under-fire owners.

At this early stage reports of Ronaldo's unhappiness are merely conjecture, but recent developments intimate both Manchester United and Manchester City will be monitoring proceedings with interest over the coming months.