There is a feeling that morale is being needlessly damaged by Mourinho's fierce complaints about the squad he has been left to work with in the US due to World Cup absentees and injuries. Up to 17 players could miss the friendly against Real Madrid in Miami on Wednesday (UK time).
There has been bemusement, for example, that Mourinho sought to publicly criticise Antonio Valencia's physical condition only days after naming him as the club captain following Michael Carrick's retirement.
Mourinho's relationship with other players is at breaking point. Anthony Martial has not returned to America after flying home to attend the birth of his second child last week and the France forward is not thought to have reacted well to the manager's claim he should still be in the US.
Sources at United believe the impact of Rui Faria's departure is already being felt as Mourinho's mood swings become more frequent. Faria, Mourinho's long-standing No 2 and a close friend, left at the end of last season to spend more time with his family and United's staff and players are ruing the absence of a key sounding board.
Although Mourinho has been installed as the joint-favourite to be the first Premier League manager to be sacked this season, he retains the support of Woodward, who has little appetite for more upheaval and handed the manager a contract to June 2020, with the option of a further year, in January.
But their relationship is facing its biggest test as United struggle to acquire the players Mourinho wants. People close to Mourinho have suggested the manager has been told he must sell before he can buy again but senior sources at Old Trafford maintain that is not the case, even though there is an acceptance that a bloated squad needs trimming.
Mourinho is desperate to sign a centre-half and has put Woodward firmly in the spotlight by claiming publicly that he gave the board "five names a few months ago". He also wants a right winger but has claimed he may have to settle for one more recruit.
There have been differences over profile of transfer targets over the past year and patience is being challenged on both sides. Brazil midfielder Fred, young right-back Diogo Dalot and third-choice goalkeeper Lee Grant are United's only signings so far.
Mourinho's dismay with United's tour extended to the manager saying he would not pay to watch his under-strength team play in the US. Charlie Stillitano, executive chairman of Relevent Sports, organisers of the International Champions Cup, defended Mourinho's remarks and accepted staging such tournaments in World Cup years was a challenge. But Mourinho's comments raised eyebrows with United's commercial staff and were considered unhelpful in terms of relations.
Nonetheless, Mourinho has had to endure plenty of setbacks in the US, which have further darkened his mood. Already deprived of half his first-choice starting XI because of their World Cup commitments, United's problems have been exacerbated by a spate of injuries on tour.
United will be without Nemanja Matic and Valencia for the start of the domestic campaign. Matic has had an operation to solve an abdominal problem and Valencia has picked up a back injury.
To worsen matters, United are likely also to be without Chris Smalling, Eric Bailly and Ander Herrera against Real. All three missed training in Miami on Monday and are unlikely to be risked so soon before the start of the Premier League campaign.
