Manchester United are treating reports that Real Madrid's Cristiano Ronaldo would welcome a return with caution amid concerns that the uncertainty surrounding him could delay a move for Alvaro Morata, sources have told ESPN FC.
There have been reports that the 32-year-old is interested in a return to Old Trafford, although Paris Saint-Germain have also been mentioned as a possible destination.
But sources said United were yet to be convinced that Ronaldo is prepared to walk away from the Bernabeu.
There is a feeling at the club that the Portugal international, who signed a new five-year contract in November, could be trying to strengthen his position at Real Madrid.
On Monday, Madrid president Florentino Perez rejected a suggestion that Ronaldo wanted the club to pay a fine that could be handed down by the courts.
"I'm sure Cristiano wouldn't want us to pay his fine if there was one -- he's not like that. If he's angry it's because he feels unjustly treated," he told Spanish radio station Onda Cero.
"Not I nor anyone at Madrid is contemplating that Cristiano could leave the club. He is not a business -- he forms part of this club's history."
Ronaldo, with the Portugal squad at the Confederations Cup in Russia, has so far remained tight-lipped.
However, his management company Gestifute have taken the unusual step of responding to enquiries about his future, if only to stress that all options are on the table.
United have always maintained that they are interested in the world's best players, but manager Jose Mourinho said in February that he did not want the club to chase "impossible deals."
Meanwhile, there is concern that Ronaldo's situation could delay United's mooted move for striker Morata.
Madrid are unlikely to commit to selling the Spain international while there remains a possibility that Ronaldo could leave.
United are in the market for a striker after releasing Zlatan Ibrahimovic and cooling their interest in Antoine Griezmann, and Morata tops their list of targets.