Last weekend, it was claimed that the 37-year-old had informed club officials of his desire to depart Old Trafford in order to play Champions League football.
While that was met with United outlining that they planned to retain the services of the Portuguese superstar, Ronaldo is yet to return to pre-season training.
United allegedly gave the player permission to miss Monday's sessions due to family reasons, although it was not expected that Ronaldo would continue to miss training up to and including Wednesday.
As it stands, it is unclear whether the legendary figure will travel with the rest of the squad to Thailand and Australia for the club's pre-season tour.
According to Football Insider, it is increasingly likely that the West Londoners will proceed with an official offer for Ronaldo over the coming days.
The report claims that Chelsea are prepared to pay a £14m transfer fee for a player who will turn 38 years of age at the start of February.
Boehly has allegedly held discussions with head coach Thomas Tuchel, who appears to have given the green light for a move for the veteran.
Despite United's disappointing efforts on all fronts during 2021-22, Ronaldo was still able to contribute 24 goals from his 38 appearances in all competitions.
Chelsea are in the market for a new centre-forward after club-record signing Romelu Lukaku was allowed to return to Inter Milan on a season-long loan deal.
In response, the Blues are on the brink of adding Manchester City winger Raheem Sterling to their ranks, the England international allegedly being informed that he will play a key role in Tuchel's plans.