The Portuguese has not taken up permanent residence in Manchester and stays at a £411-a-night suite at the Lowry Hotel while working in the city, according to The Mirror.
The club is said to be happy for Mourinho to stay at the luxury accommodation for the duration of his three-year contract, which would mean racking up a bill of more than £500,000.
Mourinho's wife and two children have remained in London while he has been spending time at the Lowry since taking charge of United last summer.
United were believed to be covering the bill for the first few weeks of his stay, but have declined to confirm whether they are still footing it.
The report goes on to say that Mourinho is unlikely to remain at the hotel for the duration of his contract and is considering moving into a flat in Manchester.