But supporters have toiled in the radio silence surrounding the deal, and now a new forward is being increasingly linked with a move to Old Trafford.
United are reportedly making a shock move for former Everton striker Dominic Calvert-Lewin after the expiry of his contract on July 1.
The M16 giants are said to believe Calvert-Lewin boasts qualities that Amorim's current attacking firepower lacks.
It is claimed that they could offer the 28-year-old free agent a lucrative contract, including bonuses for appearances, to lure him to Manchester.
United have already missed out on two top striker targets this summer after failing to qualify for European football last term.
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Liam Delap opted to join Chelsea from Ipswich Town after the Blues triggered his £30m release clause.
Viktor Gyokeres' heart also lies elsewhere in the Premier League, preferring a switch to Arsenal over a Sporting reunion with Amorim.
United accelerated their pursuit of Mbeumo in the wake of Delap going astray, but that has seemingly stalled over Brentford's demands.
Heightened noise about a potential swoop for Calvert-Lewin could indicate that Old Trafford figures are considering switching up their priorities again.
Chief executive Omar Berrada has been firm in insisting that he is determined to end United's habit of overpaying for transfer targets.
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But after two failed moves for Mbeumo, with the third likely to require over £15m in a guaranteed fee higher than the initial bid, this saga is entering that territory.
United are still strongly expected to seal a deal for the 25-year-old forward to pair him with Matheus Cunha in a new-look attack.
Amorim will not be able to make further signings beyond that without player sales, though, as the 20-time English champions work on offloading deadwood.
Marcus Rashford, Alejandro Garnacho, Antony, Jadon Sancho and Tyrell Malacia have all delayed their pre-season returns as they try to find new clubs.