José Mourinho's side brought in the Arsenal forward in a swap deal for Henrikh Mkhitaryan in January in a move which was seen as a major coup.
But Sánchez failed to fire during his first five months at the club as United failed to win silverware in a season which ended with a dispiriting FA Cup final defeat to Chelsea.
Struggling Sánchez fails to impress
The 29-year-old was a major disappointment during the second half of last season although some leeway, to allow for a settling in period, has to be given. That said, this is a crucial season for the forward with a lack of signings at Old Trafford reinforcing the onus on Sánchez to live up to his astronomical wages.
Sánchez has too often cut a frustrated figure in a United shirt and this has been apparent at times during a difficult pre-season tour for the club.
With so many players still away, following this summer's World Cup, the club's International Champions Cup squad has exposed it's limitations.
But there have been several encouraging signs which have suggested the Chile forward could deliver the return fans expected when he completed his move.
Sánchez offers glimpses of talent
Sánchez scored the opening goal in their 1-1 draw with AC Milan which was eventually won by the Premier League club on penalties.
A 4-1 hammering against Liverpool was a forgettable affair for United but Sánchez produced a virtuoso display in their final game.
Sánchez scored and set up a goal during the 2-1 win over Real Madrid in Miami which offered renewed optimism for the new season. Playing centrally, he displayed the tireless running and enthusiasm which was a hallmark during the forward's best years at Arsenal.
This looks a big opportunity for Sánchez to hit the ground running with a strong start to the season. He can have no excuses with a full pre-season behind him and no issues with fatigue after not being involved in the World Cup.
There are question marks against the fitness of some of his team-mates, after their prolonged activity in Russia, but Sánchez should be able to get off to a fast start and badly needs to after such a lacklustre opening to his United career.
Time to deliver on big stage
Sánchez only scored twice in 12 league appearances for United last season and produced three assists.
His natural flair came out only sporadically although he did manage 3.78 successful take-ons per 90 minutes which ranked the former Barcelona attacker fourth for eligible players in a similar position.
Sánchez was played out wide, mainly on the left, for United but his return of 1.63 total scoring attempts per 90 was pretty disappointing especially when compared to the 4.12 which ranked him sixth for Arsenal during the same season.
This is something which Mourinho and Sánchez will need to improve on significantly because Lukaku cannot be expected to carry the scoring burden all the time.
Sánchez‘s importance will only increase this season and it seems clear the experienced forward needs to take responsibility and influence games more if he is to be deemed a success.
Time is running out for him to win a Premier League title and even if bridging a 19-point gap to champions Man City looks a step too far, the expectation must fall on Sánchez to help deliver silverware at Old Trafford.