The Portugal international has allegedly asked the Red Devils to listen to offers for him this summer, as he wants to again play Champions League football during the 2022-23 campaign.
Ronaldo was due to return to pre-season training at the club's Carrington complex on Monday, with the 37-year-old given extra time off due to his international commitments for Portugal last month.
However, according to Manchester Evening News journalist Samuel Luckhurst, the experienced forward will not train alongside his teammates on Monday, as initially expected.
Luckhurst claims that 'family reasons' will mean that Ronaldo is absent, and the club have 'accepted this explanation'.
The 20-time English champions are due to fly to Thailand on Friday for the start of their pre-season tour, and the club are fully expecting the Portuguese to make the trip.
However, Ronaldo's desire to seek pastures new this summer has put his position in the tour squad in doubt.
"He is really disappointed by Manchester United's general situation [but] in the market especially. I'm told that Cristiano appreciates Erik ten Hag, he's convinced he's a very good manager, the right man to restart this project," Romano said on his official YouTube channel.
"But it can't be only the manager, it is needed from the club, the board and the owners – a really strong message and statement in the market. They need to sign players. I like the manager, I love the club but I don't feel the ambition. This is the message from Cristiano.
"Cristiano is really happy with some of the players in the team. But he is convinced that some signings are needed – six, seven important players are needed at Manchester United."
Chelsea, Bayern Munich, Real Madrid, Paris Saint-Germain, Sporting Lisbon and Roma are among the clubs to be linked with Ronaldo, but the journalist has said that there are not currently any firm offers.
"Cristiano has no agreement with any club as of today," added Romano. "So it is not Cristiano going to fight with Manchester United because he has a proposal, a right offer and wants to leave immediately.
"He wants to send a message, he wants to see ambition. And he wants to go in case he finds a proposal. But at the moment he has no agreement with any clubs."
Ronaldo was in impressive form for the 20-time English champions during the 2021-22 campaign, scoring 24 goals and registering three assists in 37 appearances in all competitions.