United finished second last term, their best placing since the 2013 title win in Alex Ferguson's last season in charge, but the Red Devils were a massive 19 points behind champions Manchester City and never truly in contention.
The expectation was that United would spend big in the close-season window to strengthen key areas but only Brazilian midfielder Fred from Shakhtar Donetsk and 19-year-old Portuguese full back Diogo Dalot have been added to the squad.
Barring significant late moves, Mourinho will have to rely on a similar squad to the one that was unable to keep up with neighbours City last season.
The Portuguese coach will thus be hoping his previous signings start to truly live up to expectations.
France midfielder Paul Pogba enjoyed a successful World Cup playing as a mostly defensive central midfielder in Didier Deschamps' team who became world champions in Russia.
But Pogba has struggled to find a consistent role at United and it will be interesting to see if Mourinho takes a leaf out of Deschamps' book and asks less of him in terms of attacking support for his team's front line.
Chilean Alexis Sanchez, a January signing from Arsenal, never really settled during the second half of the season but after a summer's rest due to his country's absence from the World Cup, he should be refreshed and better integrated.
Striker Romelu Lukaku showed his all-round quality in Belgium's run to third place at the finals and proved he can offer more than being just a battering ram target.
If Pogba, Sanchez and Lukaku click together, United have the potential to be an exciting team going forward with Fred offering help to Nemanja Matic in the centre of midfield.
United's defence was solid last season, second only to City in conceding just 28 goals, but the hope was that they could add a ball-playing central defender to help develop a more fluent style from the back.
The club's pre-season tour of the United States has hardly increased confidence in Mourinho's project.
The former Chelsea and Real Madrid boss has been in a downbeat mood - suggesting frustration at the lack of incoming players and a less than satisfied attitude towards his squad.
With several key players returning to training late after their efforts in Russia, Mourinho has not been able to test-drive his first-choice team.
Perhaps the final days of the transfer window will bring the kind of reinforcements that will satisfy him but as it stands it is hard to escape the feeling United will again be in the top four without the quality to go all the way.
(Reporting by Simon Evans; Editing by Ken Ferris)
