According to The Sun, the Portuguese boss was left furious when he learned that the Reds will be playing at Anfield after all six of their UEFA Champions League group matches this autumn - unlike Manchester City, Tottenham and the Red Devils, all of whom face three home fixtures and three away from home after their respective group matches.
This obviously means that Jürgen Klopp's side will have to do less travelling after their European clashes. Moreover, any fatigue or injury issues which arise in the Champions League will likely be mitigated by home advantage in their subsequent Premier League fixtures.
Nevertheless, neither City's Pep Guardiola nor Tottenham's Mauricio Pochettino are believed to be upset about this apparent advantage for the Reds. Besides, Mourinho has a long-established history of complaining about fixtures.
A cynic might suggest that the United boss is getting in his excuses early, as his side face extremely stiff competition for the Premier League title - which would be the Red Devils' first in six years, were they to win it.
Against reigning champions Manchester City, a consistently impressive Spurs side and a rejuvenated Liverpool - as well as Chelsea and Arsenal, who will be hoping for significant improvements on last season - even a top four finish is unlikely to be a formality for Mourinho's side.
United finished second in the Premier League last season but trailed the Citizens by 19 points, as well as being routinely criticised for their negative playing style. Nevertheless, the Red Devils will no doubt draw encouragement from the fact that they were one of just two sides to defeat Guardiola's charges in the league - the other one being Liverpool.