Ronaldo is eyeing a departure from Old Trafford, having been dropped to the bench by manager Erik ten Hag in United's past five league outings.
The Dutch tactician reportedly held a meeting on Monday (3 October) where players and staff were given the go-ahead to scrutinize one another.
It came after the Red Devils' disappointing 6-3 defeat to Manchester City in the Manchester derby on Sunday.
Ronaldo played no part in the derby and instead cut a frustrated figure from the substitutes bench while watching his side get dismantled.
Ten Hag has always stood by the club's stance that Ronaldo is not for sale but is now believed to be open to allowing the veteran striker to leave in January.
The Manchester United boss had wanted to retain the Portuguese forward when he first took over at Old Trafford.
However, Ronaldo's desire to leave the club has lingered and with that, Ten Hag has become more relaxed about losing the former Real Madrid attacker.
The five-time Ballon d'Or winner was keen to join a side contending in the UEFA Champions League this summer.
The only offer that came in for his services was from Saudi club Al Hilal.
Ronaldo has made eight appearances for the Red Devils this season, scoring just one penalty in a 2-0 win over Sheriff Tiraspol in the UEFA Europa League.
The legendary forward has a year left on his contract with the option of a 12-month extension.
Manchester United finally cater to Cristiano Ronaldo's desire to leave
Manchester United seem to have finally accepted that Cristiano Ronaldo is better off departing the club.
The question now is which potential suitors will come in for the forward if he is indeed on the market this January.
Chelsea, Bayern Munich and Atletico Madrid were all touted with moves for Ronaldo in the summer but none made any of their supposed interest concrete.
Ronaldo's performances for both club and country have drawn criticism this season. But so did Ten Hag's decision to leave him on the bench against City.
Ten Hag claimed that he didn't want to bring him on out of respect for his huge career.
However, the forward played the entirety of Manchester United's demoralizing 4-0 defeat to Brentford on 13 August.
The first source claimed that Cristiano Ronaldo has remained professional throughout the ongoing saga surrounding his future.
Yet, the Portuguese has always seemed dissatisfied with staying at Old Trafford, especially in the current role he has been given.