Here, AFP Sport looks at whether Ole Gunnar Solskjaer can make United a contender again for the first time since its last Premier League title in 2012-13 or whether it is facing another season of turmoil and pain.
What to expect
It is difficult to know what to expect from Solskjaer's United, which enjoyed a purple patch after the Norwegian replaced Jose Mourinho but slumped alarmingly toward the end of last season.
At one stage it looked likely to finish in the top four but there was the suspicion it was getting the rub of the green and so it proved.
United’s campaign ended with a whimper as it drew 1-1 at relegated Huddersfield and then was beaten 2-0 at home on the final day by Cardiff, which was also heading out of the Premier League.
A gap of 32 points to champion Manchester City was embarrassing and many questioned whether the club had been too hasty in appointing the relatively inexperienced Solskjaer to the fulltime manager's post.
United will not have Champions League football to paper over the cracks during the coming season, with Thursday nights in the Europa League ringed in the calendar instead.
The club has had a positive preseason but there are still lingering issues that need to be addressed – Paul Pogba's future is still in doubt and Solskjaer has to wrestle with the conundrum of an under-performing Alexis Sanchez.
United had problems at both ends of the pitch last season – scoring 30 goals fewer than City in the Premier League and conceding 54 goals, the most it had conceded in a league season since 1978-79.
The 20-time champion desperately needs a positive start to rebuild confidence that it can challenge at the sharp end of the Premier League.
Anything less and the knives could be out for Solskjaer.
After a leaky defense played a key role in United's struggles last season, Solskjaer made it clear he wanted Leicester's Harry Maguire to plug the holes.
The England center-back is reportedly on the verge of becoming the world's most expensive defender, with United said to have agreed an £80 million fee to land Maguire.
But has it signed enough faces to boost a squad that looked short of class compared with Manchester City and Liverpool last season?
Highly rated right-back Aaron Wan-Bissaka has joined from Crystal Palace, with Solskjaer describing the 21-year-old as "one of the best upcoming defenders in the Premier League."
Winger Daniel James was bought from Championship club Swansea to add thrust on the flanks.
United has also been linked with a swoop for Juventus forward Paulo Dybala, but the Argentine is said to be unsure about joining a team outside the Champions League.
Romelu Lukaku could be on the way out of Old Trafford, with Juventus and Inter Milan both keen on the Belgium striker according to reports.
This is the season when Marcus Rashford will have to step up and show emphatically that he deserves to wear the number 10 shirt at Manchester United.
Still only 21, Rashford scored 17 goals in 54 appearances last season for club and country but will have to boost those numbers if he is to be the undisputed leader of United's attack.
Rashford signed a new four-year deal to remain at Old Trafford last month, saying it was "a privilege" every time he wore the shirt.
He has scored some sublime goals for the club but with a shortage of goal threat from elsewhere, Solskjaer will want to see him take his tally to 20-plus goals this season and become more of a poacher.
Solskjaer insisted on Saturday he has "no doubts at all" that Pogba is committed to Manchester United.
French World Cup winner Pogba was missing from the United squad for the preseason penalty shootout win over AC Milan in Cardiff.
However, Solskjaer insisted the star's absence was due to a "back spasm."
When asked if Pogba was set on staying at United, the Norwegian said, "I've no doubts at all.
"I wasn't expecting him (on the plane to Cardiff). I spoke to him after training and he didn't feel right.
"Paul will probably be back early next week training. It's not an injury, he just felt some pain. We didn't want to risk anything this weekend and he should be OK for Chelsea next week."