The Times says United boss Sir Alex Ferguson is known to have been angered by the player's poor timekeeping, with Hargreaves turning up late for several team meetings.
Signed for a projected fee of £20.2 million from Bayern Munich last summer, Hargreaves has found himself fourth or even fifth choice in central midfield as United chase Barclays Premier League and Champions League trophies.
While speculation has centred on whether Ferguson is unconvinced by the England international's form, it is understood that the manager has been punishing Hargreaves for what he perceives as a slovenly attitude.
One source said of Hargreaves's indiscretions that "it might only be a matter of being 20 seconds late, but that is too late as far as the manager is concerned and he [Hargreaves] knows he is either going to have to adapt or face the consequences. It's a learning process for him, but he will adapt and he has told the manager that, which should be the end of the matter."