The Portuguese superstar wants Jorge Mendes to “do everything possible” to make the move happen.
The forward faces allegations of a £13million tax fraud and now doubts over his Real future have sparked a megabucks scramble for his services.
United, Chelsea, Paris Saint-Germain and Bayern Munich are all potential suitors.
PSG are prepared to offer £122m to land him plus a staggering salary of £26m per year to persuade him to switch to the French capital.
But Ronaldo is keen to return to United and has instructed his representative, fellow Portuguese and super-agent Mendes, to do everything in his power to make it reality.
The 32-year-old is understood to feel he had unfinished business at Old Trafford and cannot miss out on the chance to return as a hero.
One issue which will need resolving is his complicated relationship with United boss Jose Mourinho.
The pair fell out during Mourinho’s final season at the Bernabeu but they are both on Mendes’ books.
And the United chief is willing to bury the hatchet to bring in Ronaldo’s goals and personality.
Ronaldo has ignored pleas from Real boss Zinedine Zidane to reconsider his position.
And his belief that it is time to move on has strengthened over the past three days.
Ronaldo added fuel to the fire yesterday when he dodged media duties after a dazzling display in Portugal’s 2-2 draw with Mexico in Kazan at the Confederations Cup.
Instead, after a “flash” interview — where he took just three questions — the Portuguese FA confirmed he would not be picking up his man-of-the-match award as he was “having treatment”.