The number conveys greatness at Old Trafford. George Best, Bryan Robson, Eric Cantona, David Beckham and Cristiano Ronaldo were Manchester United's great No. 7s. More recently, Angel Di Maria and Memphis Depay were great disappointments.

The temptation to put Alexis Sanchez into the same bracket should be resisted. Yet, 10 games into his Old Trafford career, what can be said is that the Chilean is United's great complicator. Complications have abounded since he and Henrikh Mkhitaryan swapped clubs in January, and not just because his sizeable salary could mean future recruits demand similar remuneration and even United's huge budget gets stretched. Those complications are rarely Sanchez's fault, but they are a consequence of his arrival.

Jose Mourinho resolved them for 90 minutes against Brighton by reverting to the recent past. He benched Sanchez and named the sort of side he might have picked two months ago. Anthony Martial started and Marcus Rashford came off the bench. The Frenchman and the Englishman had shared the duties on the left before the arrival of the Chilean from Arsenal altered the equation.

If their part-time roles seemed a short-term solution, Mourinho nevertheless showed a capacity to compromise and a strategic grasp of the numbers to afford each plenty of minutes. It became a productive case of juggling: Mourinho's capacity to inject speed against tiring defenders -- and Martial had a spell as a particularly prolific substitute -- accounted for many of United's rash of late strikes. Between them, Rashford and Martial clocked up 20 goals by the end of January; not quite Mohamed Salah-esque, but potent nonetheless. All 20 goals weren't delivered with Martial or Rashford playing as left wingers, but the majority were.

In the Sanchez era, however, Martial has regressed and is yet to score. Rashford has three goals: one as a striker against League Two Yeovil Town and a match-winning double against Liverpool on the one occasion he has been unleashed to start on the left.

It has been harder to accommodate both, partly because of Mourinho's reluctance to deploy either as a striker in a major match. Sanchez delivered most of his 30 goals for Arsenal last season as the front man but is far too short to be an archetypal Mourinho target man. It all suggests that, with Zlatan Ibrahimovic on the way out and Mourinho claiming that no attacker will be brought in during the summer, a by-product of Sanchez's signing will be that the already huge workload Romelu Lukaku shoulders will grow.

Alexis Sanchez's early days at Man United have not gone as planned under Jose Mourinho. no_source

Because there is a lopsided look to the front four. United's six attackers next season could be three players Mourinho regards as left wingers, one striker, one No. 10 and one right winger who is a converted No. 10. Bringing in Sanchez has cemented the feel of an expensive imbalance to the squad, with too many players in some positions and too few in others.

Versatile as Sanchez and Rashford, who began on the right against Sevilla, are, Mourinho does not seem to deem either at his best on the right. That is understandable: Sanchez's signature move can be to cut in from the left and shoot. Mkhitaryan, in contrast, had the positional profile the squad needed: he could operate on the left, liked being in the middle and was a more natural choice on the right, where he flourished for Dortmund. Instead, Juan Mata, scarcely a conventional winger, is now the nearest thing to a specialist on that side.

In theory, Sanchez's ability to operate directly behind Lukaku is another boon. Arguably his most effective display for United, against Liverpool, came in that central berth. Yet before his arrival, Jesse Lingard produced the finest form of his United career; largely, though not exclusively, as a No. 10. His goal at Yeovil was his ninth in 13 games; there has only been one in nine since, and three of those subsequent appearances have been as a replacement. It jarred with the sense of meritocracy to see Lingard demoted so swiftly.

The knock-on effects may stretch to United's other demoted superstar. If, before Sanchez and Paul Pogba manned the bench together, they were twinned in underachievement, the question persists if they are complementary talents. There is a theory the Frenchman is at his best in a 4-3-3, liberated from some defensive duties and free to roam forward into the inside-left channel; that also may be where Sanchez ends up when he veers infield.

United may have played 4-2-3-1 too often, especially away from home. It is a result of both midfield injuries and trying to cram in forwards. It reflects a squad overloaded with both attackers and A-listers. It muddles selection and demotion alike when status and salary become factors. Pogba is proof that it will always be a bigger issue to omit players of a certain cost, past or profile. It implies that potential is not being realised, that major decisions were misjudged, that grand strategies have backfired. At United, where the scale of resources is not matched by the skill of planning, that is amplified.

Sanchez's arrival was abnormal, a product of opportunism when he became available, a case of strengthening while weakening one rival and preventing other peers from getting better. United had less time to consider the consequences.

Yet those 10 games have illustrated the issues extend beyond some indifferent displays, a meagre return of one goal and the question of chemistry. That does not necessarily doom Sanchez to failure at Old Trafford, but confused thinking has created complications with positions and personnel, tactics and supposed talismen, squad balance and future signings. It is no simple task for Mourinho to resolve them.