The Portuguese star is said to be keen to play Champions League football this season and is reportedly unhappy with United’s relative lack of transfer activity this summer after a sixth-place finish in the Premier League.

Chelsea, Bayern Munich and Napoli are among a number of clubs that have been linked with Ronaldo, while a potential transfer to Paris Saint-Germain has also been touted as another possibility for the five-time Ballon d’Or winner.

A move to the Parc des Princes would see Ronaldo link up with his long-time rival Messi, who is preparing for his second season at PSG.

It would be an unlikely partnership between the two players, who rivalled each other for individual and team honours throughout their time in Spanish football when Messi was at Barcelona and Ronaldo played for Real Madrid.

Back in 2015, Messi was asked about the prospect of playing in the same team as Ronaldo and whether it would be something he would agree to.

Messi has previously said he would like to play Ronaldo (Image: Alamy)”Yes, of course,” the seven-time Ballon d’Or winner said.

“I always like to play with the best, and he is one of them. I think it will be difficult for us to play in the same team, but obviously I would like to.

“I was lucky enough to play and participate with many very good players and, obviously, I would also like to do it with him.”

The two players have rivalled each other for honours for more than a decade (Image: Alamy)Ronaldo’s agent Jorge Mendes recently met with Chelsea co-owner Todd Boehly to discuss a potential deal for the Portugal international.

However, Blues head coach Thomas Tuchel is said to have ‘little interest’ in signing Ronaldo, with the London club close to completing a deal for Manchester City forward Raheem Sterling.

It remains to be seen whether a suitable offer will arrive for Ronaldo before the start of the season, with United due to face Brighton in their opening Premier League match on August 7.