Spanish media sources have revealed that Ronaldo (right), contracted to the Bernabeu until 2015, is sitting on his hands despite several improved offers from Madrid.
Alex Ferguson suggested just a week ago that while he would love to have Ronaldo back, he could see not see a way past the enormous £170m buy-out clause.
But Real Madrid must now face the possibility that Ronaldo will mark time until the end of his contract in 2015 and leave as a free agent.
Their best option is to put him on an auction block and sell him to the highest bidder, with PSG ready to stump up £80m.
However, if Ronaldo is committed to a return to Old Trafford, he need only dig his heels in and refuse all offers until Madrid agree to do a deal with Manchester United.
The news comes amidst heightened speculation that Robert Lewandowski will sign for Ferguson next June in an £18m move from Dortmund.