Manchester United's capture of Alexis Sanchez from Arsenal may come to define manager Jose Mourinho's time at the club.
There is no doubting the Chilean forward's talent but his task now is to take United to a level where they can challenge Pep Guardiola's runaway Premier League leaders Manchester City, something that has been beyond them so far this season.
In signing Sanchez, Mourinho hopes he has captured the sort of energetic creativity missing from United this season.
While Henrikh Mkhitaryan, who has moved the other way, is a thoughtful, sometimes inspired player, Sanchez is a firecracker. He can fizz past defences and will get the Old Trafford fans off their seats like George Best and Ronaldo once did.
Naysayers questioning the deal fear Mourinho, the ultimate short-termist, has recruited someone who, at 29, is beyond his best. They note that Sanchez has played more than 50 games for seven consecutive seasons, a heavy load on even younger legs.
Whatever the future, Sanchez belongs with a select band of players like Eden Hazard, Kevin De Bruyne and Philippe Coutinho who have been proven Premier League game changers.
While his strike rate in the league over 3-1/2 seasons at Arsenal is almost one in two, his statistics this term are less impressive. In a year when the club have struggled, his goal conversion rate of seven from 69 shots reflects many factors, not least a tendency to shoot too often from outside the area.
For the past year he has appeared a brooding presence at Arsenal, arms often flung wide and head thrust back as another move broke down on the edge of the penalty area.
The move to United has freed him from the frustration of playing in a failing Arsenal team from whom many have sought an exit route.
United believe the deal represents good business because they have snaffled a reported 100 million pounds player by exchanging him for one they no longer wanted. Even paying Sanchez his reported 70,000 pounds ($97,699.00) a day wages does not take the overall deal beyond what has become the norm for the league's leading clubs.
Equally, it is no surprise that City baulked at the figures, preferring not to destabilise their whole wage structure in a season when the league title is already all but guaranteed.
Finishing second would represent progress for United, who will now look for Sanchez to give the whole club a lift.
But there are also risks attached to recruiting a player mid-season and Mourinho's first task is to decide who to leave out of a team that has not been doing too badly.
With Anthony Martial and Marcus Rashford competing for a place on the left, Sanchez may find his most natural position, where he cuts inside on to his right, is blocked so a berth on the right, at Juan Mata's expense, is more likely.
That would leave the Spaniard scrapping with Jesse Lingard for a more central role behind United's main striker Romelu Lukaku while powerful midfielder Paul Pogba stays further back.
It is the sort of dilemma Mourinho came to Old Trafford for. But, having dispensed with Mkhitaryan, a player expensively recruited on his watch, the demanding Portuguese coach knows he must get the mix right this time to please his paymasters.