According to the UK Sun, the group is concerned that it may stymie their growth.
Mason’s attempted rape and assault charges were dropped this week.
However, the 21-year-old is still under investigation by the club.
Greenwood is still on United’s Premier League team after being picked as one of their U-21 players at the start of the season.
“The players are open to him returning to the club, but the attention might be immensely distracting,” a source added.
“The dressing room is the happiest it’s been in ages, and no one wants to upset the apple cart.”
United are in good form under new manager Erik ten Hag, and they now sit third in the Premier League rankings after a 2-1 victory over Crystal Palace on Saturday.
Greenwood last played for United in January 2022, and he is under contract with the club until 2025.