The Red Devils finished sixth in the Premier League in 2018-19 and failed to win any silverware.
They enjoyed a 10-week purple patch immediately following Ole Gunnar Solskjaer's appointment as Jose Mourinho's successor in December when they won 14 of 17 matches in all competitions.
But a five-game winless run to close out the Premier League season meant they finished outside the UEFA Champions League spots.
To make matters worse, Manchester City won a domestic treble, while Liverpool and Chelsea won European titles, beating Tottenham Hotspur and Arsenal, respectively, in the Champions League and UEFA Europa League finals.
One of the few bright spots for United last term was Shaw, whose consistent performances earned him the club's Player of the Year award.
As far as the Englishman is concerned, though, nobody deserved the gong as it was such a disappointing campaign, per Adam Bate of Sky Sports:
"From a personal point of view, it was a better season than I have had for a while, but I still think I can do much better. I didn't really feel like anyone deserved the player-of-the-year award because of the season we had as a team. There is more to come from me, and everyone needs to be better because last season was somewhere near embarrassing.
"It hurt even more that there were so many English teams around us who were playing in finals and had done well while we were just on holiday. There was nothing we could do about it other than watch the games and think. Of course it hurt. We all felt it. We have a lot to prove this season, and I am sure we will. We are going to have a much better season."
Shaw, 24, should be a key part of a new-look United defence in the 2019-20 campaign.
David De Gea will remain No. 1, Shaw will continue at left-back and Victor Lindelof will likely be among the starting centre-backs.
But new signings Aaron Wan-Bissaka and Harry Maguire should complete the back line of what United will hope is a more frugal side:
The Manchester giants conceded 54 goals in the Premier League last term, their worst record since 1978-79 and an unacceptable tally for a club that should have title ambitions.
United will have to be at their best early on in 2019-20 as they face Chelsea in their Premier League season opener at Old Trafford on Sunday before a trip to Wolverhampton Wanderers, who they failed to beat once in three meetings last term.