Greenwood has established himself as an important part of Ole Gunnar Solskjaer's first-team plans at Old Trafford, scoring 17 goals in 49 appearances during a breakthrough campaign last term.
The 19-year-old has scored once in four outings so far this season, but has been left out of the last two matchday squads due to an unspecified fitness issue.
Solskjaer denied that off-field reasons were behind Greenwood's absence, but the Daily Mail claims that staff at the club have become increasingly frustrated by the youngster's "general tardiness".
The England international has subsequently been given a talking-to by members of the United hierarchy, although Solskjaer hinted that he could be back available for Saturday's showdown at home to Chelsea.
Greenwood was also caught up in a disciplinary storm while away with England last month when he and Manchester City's Phil Foden broke coronavirus protocols by inviting two girls to the team hotel in Iceland. body check tags ::