Sir Alex Ferguson took 20 seconds to block Cristiano Ronaldo's Man City transfer

If Manchester United are to take anything from this Saturday's derby with Manchester City, it will likely be thanks to Cristiano Ronaldo.

However, the Daily Star report that without a brief and very pointed phone call from Sir Alex Ferguson, the outcome could have been very different.

Ronaldo has only been back with the Red Devils for just over two months, but the 36-year-old has already re-established himself as the club's true talisman after a 12-year absence.

His return to Old Trafford was one of the standout moments in one of the most memorable transfer windows in recent history.

HAVE YOUR SAY! Was Cristiano Ronaldo to Man Utd the best deal of the summer? Let us know your thoughts below

Cristiano Ronaldo has nine goals in just 11 games since his stunning summer transfer

Weeks after his old foe Lionel Messi had completed his own earth-shattering move, Ronaldo was plotting to do the very same.

Unhappy with his situation in Juventus, the Portuguese legend and his agent Jorge Mendes were quietly sounding out destinations for a blockbuster transfer.

A return to Real Madrid was touted, potentially joining Lionel Messi at Paris Saint-Germain was even suggested as an option.

Cristiano Ronaldo has nine goals in just 11 games since his stunning summer transfer

In six seasons in the Premier League, working under Sir Alex Ferguson, the tricky winger, known for his flamboyant stepovers lifted the title on three occasions.

After a gentleman's agreement between player and manager, Ronaldo was allowed to leave the club, joining Real Madrid where he would go on to become one of the greatest goalscorers in the history of the game.

But for fans, there was always a lingering feeling that the special son would at some point return to The Theatre of Dreams to help propel his old side back to former heights.

Sir Alex Ferguson made his feelings about Ronaldo going to Man City clear ( Image:

Matthew Peters/Manchester United via Getty Images)

So when rumours claimed their favourite son could don the sky blue of Manchester City, it sent fans, former players and pundits into overdrive.

Patrice Evra and Rio Ferdinand both made contact with the five-time Ballon d'Or winner, but as he boarded the plane in Turin a move to the Etihad looked on the cards.

City had already agreed a £25million deal with Juventus and chiefs were confident of getting a deal over the line.

However, Star Sport reveal that a 20-second intervention from Sir Alex turned the tide and ensured his triumphant return would be sealed.

Will Ronaldo be the decisive factor in Saturday's Manchester Derby? Make your predictions below

The report suggests that Ferguson rang his old charge directly and simply said, "don't join City" before hanging up.

That reportedly made it clear to Ronaldo that United bosses were just as keen as City to land the superstar and the decision became a formality.

Just days later, Ronaldo signed on the dotted line to become a Manchester United player again, in potentially the most dramatic transfer U-turn in Premier League history.

City will get a first-hand glimpse of just how costly that brief call was when he lines up as a red when he was so close to being a blue.