Former Manchester City striker Niall Quinn has warned Cristiano Ronaldo that he would be "putting everything at risk" if he left Real Madrid to make an Old Trafford return.
The Portuguese superstar has been repeatedly linked with a switch back to former club Manchester United, having reportedly grown tired of life in the Spanish capital.
Quinn, who spent six years playing for United's city rivals, believes that Ronaldo would be better off choosing fellow reported suitors Paris Saint-Germain if it were a choice between the two European giants.
"There is a risk," he told Sky Sports News. "The commercial guys would love it but I think his longevity staying at the top of his game for as long as possible would be better served by staying at Real Madrid.
"If he comes to United, he's putting everything at risk. Stats will tell you, doing it for a second time at a club is difficult."
Ronaldo spent six years with the Red Devils before moving on to Madrid in a then-record £80m transfer in 2009.
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