After spending some time off unwinding with family in Ibiza, the five-time Ballon d'Or winner was expected back at United's Carrington training base to start his pre-season training on July 4. Instead, Ronaldo informed the club he would not be in attendance and cited family reasons as the explanation behind his absence.
It was the same story the following day, meaning he has now missed his first two days of scheduled pre-season training.
The Athletic reports some within the United hierarchy feel let down by the fact Ronaldo was well aware the Red Devils had missed out on Champions League qualification in early April, but stayed silent before informing them of his wish to leave as late as July.
A source close to Man United told the publication some believe his timing to be "awful".
Others are fearful that he could cause further embarrassment to United by refusing to attend their pre-season tour of Thailand and Australia.