While Jose Mourinho's side climbed from sixth to second in 2017-18, the style of football left many supporters dissatisfied and the team still finished a record 19 points adrift of champions and local rivals Manchester City.
The summer transfer window started brightly for the Red Devils, bringing in Fred and Diogo Dalot early, but it soon descended into frustration and - at times - seemingly desperation as Mourinho tried to bring in defensive reinforcements.
In the end United missed out on their main targets, and they must now look to close that sizeable gap to their Manchester rivals - in addition to holding off renewed challenges from those below - knowing that they have not strengthened as much as they would have liked.
Here, Sports Mole looks at how United could line up in 2018-19.
Transfers in: Diogo Dalot (£19m, Porto), Fred (£47m, Shakhtar Donetsk), Lee Grant (undisclosed, Stoke City)
Transfers out: Michael Carrick (retired), Joe Riley (undisclosed, Bradford City), Dean Henderson (loan, Sheffield United), Sam Johnstone (£6.5m, West Bromwich Albion), Daley Blind (£14m, Ajax), Matty Willock (loan, St Mirren), Cameron Borthwick-Jackson (loan, Scunthorpe United), Joel Pereira (loan, Vitoria Setubal), Axel Tuanzebe (loan, Aston Villa), Timothy Fosu-Mensah (loan, Fulham)
The whispers of David de Gea leaving United for Real Madrid look to have finally abated following Thibaut Courtois's move to the Bernabeu, and the Spaniard will once again be the undisputed number one for the Red Devils this season when he will look to further enhance his reputation as arguably the best goalkeeper in the world.
United were hoping for more change in front of him, though, and their failure to bring in a new central defender in particular could cost them this season. Interest in Toby Alderweireld, Harry Maguire, Diego Godin and Yerry Mina all came to nothing, leaving Mourinho with the same defensive options as last season - minus the departed Daley Blind.
Phil Jones, Victor Lindelof and Marcos Rojo will hope to challenge Eric Bailly and Chris Smalling for a starting role at the heart of the defence, while Luke Shaw has once again stayed at the club but remains behind Ashley Young in the left-back pecking order. New arrival Dalot should eventually provide competition for the ageing Antonio Valencia, but for now the new United skipper remains first choice.
The arrival of Fred represents United's headline summer signing, and the Brazil international should add further dynamism to a midfield already including Nemanja Matic and World Cup winner Paul Pogba. Pogba in particular will be under scrutiny this season after impressing for France in Russia, despite coming off the back of an underwhelming 2017-18 campaign at club level.
Juan Mata, Ander Herrera, Marouane Fellaini and Scott McTominay are all likely to feature in bit-part roles again, while Andreas Pereira could become a more regular feature in the team this season following spells out on loan.
Romelu Lukaku's World Cup exploits mean that he will miss the start of the season, but he remains United's first-choice striker after 27 goals during his first year at the club. Jesse Lingard also made it to the final week of the World Cup with England and will be hoping to build on what was a breakthrough campaign for him last term.
There will be plenty of interest in the performances of Alexis Sanchez too, with the Chilean having struggled to impress since his January move but also being fresh for the new season after a rare summer off. Marcus Rashford and Anthony Martial provide further attacking options, but both could once again face extended time on the bench this season.