The Portugal international has asked the club to accept any satisfactory offer after declaring his determination to play in the Champions League.
United insist he is not for sale and expect him to see out the final 12 months of his contract – but his absence from their travelling party for the tour of Thailand and Australia for "family reasons" adds to the uncertainty surrounding his future.
And if he is successful in convincing United to sell, it will force Erik ten Hag to bring forward his plans to sign a top class centre forward by 12 months.
While United had targeted Darwin Nunez, their failure to beat Liverpool to the Uruguayan saw them decide to wait until next summer to look for a replacement for Ronaldo.
One of the biggest issues is a budget that has to be focused on other parts of the squad, with around £55 million ($65m) needed to land top target, Frenkie de Jong.
United are hoping to sign Ajax winger, Antony, for around £50m ($60m) – and team-mate, Lisandro Martinez, could cost in the region of £40m ($48m).
It would take vast amounts to sign the calibre of striker required to replace Ronaldo, while the lack of credible options on the market is another issue.
Consequently, Ten Hag will have to weigh up both internal and external striking solutions if he can’t convince his star man to stay for one more season...
.jpg?auto=webp&format=pjpg&width=640&quality=60)