Farewell number 18, hello number six - inside Man Utd's midfielder hunt

The acquisition of a new central midfielder is viewed as the priority for Manchester United this summer.

Elliott Anderson, Carlos Baleba, Adam Wharton and Sandro Tonali are all targets to replace the outgoing Casemiro.

In a nutshell, it is farewell number 18 as the Brazilian departs and hello number six - the crucial, modern defensive midfielder the Old Trafford club want to replace him with.

But it is never that simple.

Here, BBC Sport looks at how United's search is shaping up.

There are two key factors linked to that hunt that require settling before United can map out their path towards signing Casemiro's successor.

First of all, Champions League qualification will be a crucial element.

Players are still attracted to United regardless of European qualification. The fact Bryan Mbeumo, Matheus Cunha and Benjamin Sesko - who all had Champions League interest last summer - chose United without the guarantee of playing in the continent's top club competition is testament to that.

Nevertheless, it remains a lure for the very top players, while the monetary benefits that stem from qualifying for the tournament will help ease the financial burden on paying for such stars.

Then, of course, is the matter of who becomes United's permanent head coach.

Michael Carrick is doing his hopes of landing the job on a full-time basis no harm.

If he can lead the club to a top-four finish he will confirm his serious candidacy, though the attraction of appointing a proven 'elite' head coach should not be underestimated as United decide the identity of their next boss.

But regardless of who is in the dugout, the need for a new number six is pressing with work towards identifying targets well under way.

Nottingham Forest's Anderson is viewed internally by many at United as the player the club should prioritise.

The midfielder has excelled from a personal perspective in spite of Forest's struggles this season. His performances - barring an unexpected turn of events - have secured the 23-year-old a starting berth in the England team for this summer's World Cup.

It is likely Anderson would cost a minimum of £80m - a fee United accept they will need to pay to secure one of their top targets for the coveted number six position.

However, there is a significant obstacle in the way of United's interest in Anderson - Manchester City.

Multiple sources have told BBC Sport that City are the clear frontrunners to land Anderson at the end of the season.

That is not to say United will abandon their interest.

While United would be wary of getting involved in an auction over wages with their city rivals, they are prepared to make a substantial effort to sign Anderson.

And while many of the early indicators point towards Anderson, who has also attracted interest from Bayern Munich, moving to Etihad Stadium, United can point to the fact that Sesko appeared close to joining Arsenal or Newcastle last summer only for the striker to eventually land at Old Trafford.

But, for obvious reasons, United are not putting all their eggs in the Anderson basket.

While United are not discounting looking abroad in their search for a new lynchpin, the club would prefer Premier League experience.

Deciding to go for proven players would certainly limit United's options, and ultimately increase the finances attached to those deals.

Baleba, Wharton and Tonali are also among the players United's recruitment team have discussed and will continue to explore.

One well-placed source has told BBC Sport that, via an intermediary, United have made a tentative enquiry about Brighton midfielder Baleba in recent months.

However, any successful move for the Cameroonian will depend on Brighton's valuation, which reports suggest is £100m.

While United accept they will have to make a massive financial outlay to land one of their preferred midfielders, whether they would be willing to match the sort of fee Brighton will be looking for is in question.

Crystal Palace's Wharton is certainly admired at United, but whether he fits the sort of profile the club are looking for is unclear.

Wharton is viewed as a player who benefits from having runners alongside him in midfield, allowing him to execute the passes that have become synonymous with his burgeoning reputation as one of England's best emerging talents.

Palace have explored the possibility of offering Wharton - whose contract has three years to run - a new deal with a release clause in the hope of securing his future before next season.

Similarly with Tonali, Newcastle have a history of making things difficult for clubs interested in their players. Just ask Alexander Isak and Liverpool.

But there is a suggestion the Italy midfielder is open to leaving St James' Park this summer, with his representatives understood to be scoping out the market to ascertain which clubs may be interested.

Outside the Premier League, Atalanta midfielder Ederson is among the players in Europe who club recruitment staff have identified as having potential.

There is a world in which United look to sign two number sixes, particularly if Manuel Ugarte leaves - which is possible this summer - though in such a scenario it is very likely the second capture would be rotated more than their primary signing.

The expected exits of Rasmus Hojlund and Marcus Rashford this summer will help supplement United's transfer budget, which will also need to stretch to signing a left-winger and potentially a central defender, though that would depend on the outcome of the Harry Maguire's talks over a new deal.

But the number six is set to be the big one to watch.