Here is a full list of summer transfers in 2015. It's getting pretty busy now...
Like an elderly, grumpy cat that has given up its duties as a family pet and now expects to be able to do exactly as it pleases in its twilight years. It's Mark Lawrenson...
Surely the most popular man to get the gig with United supporters?
Borussia Dortmund have certainly struggled at times this season after a phenomenal period that brought two league titles and a Champions League final appearance, but a quick glance at the club's injury list over the past few months provides a worthy excuse, as does the all-conquering Bayern Munich side that Klopp has been forced to pitch himself against.
This is a manager that has dealt with the departure of star players and yet still managed to sculpt one of European football's most exciting attacking sides. Picking Dortmund up from their lowest ebb, Klopp transformed an ageing side into a vibrant, ball-playing team and brought the fans under his spell and closer to their club than they had ever felt, a task certainly required at Old Trafford. Hell, he even got the best out of Shinji Kagawa.
What's more, Klopp may finally fancy a change after losing Robert Lewandwoski to Bayern this summer. The suspicion is that the manager may have reached the stage where, at 46, he feels held back by life in Westfalia, and with Europe's biggest clubs ready to knock on his door, United could position themselves at the front of the queue. The only evident drawback appears to be the inability to promise Champions League football, but Klopp is a coach that appears charmed by the idea of a long-term task.
This is a coach who has taken on the financial clout of Real Madrid and Barcelona and is closing in on an extraordinary victory in that battle. If he completes a La Liga and Champions league double, Diego Simeone will have overseen one of European football's most impressive seasons in living memory. In comparison, competing against the economic muscle of Manchester City and Chelsea would seem like a walk in the park.
One of Moyes' biggest problems at United was his inability to inspire his players, failing to get them to either believe in his mission or fight in response to things going astray, and this is where Simeone thrives. The Argentinean demands respect, passion and determination, and insists that his squad fight to the end for themselves, the manager and the club.
Furthermore, Simeone could never top this season at Atletico, and so may be tempted by a change after two-and-a-half years in Spain. Real Madrid will invest once again and Barcelona will surely not be so weak in the near future. Could United lure a coach with a sugary-sweet financial package, transfer budget far beyond his current expectations and the promise that he will be given time to rebuild one of European football's powerhouses?
Perhaps the sentimental choice, but certainly one that would sit comfortably with United's desire and clamour for stability and sustainable development. Giggs is currently still completing his coaching badges, but could take the summer to get everything in administrative order.
David Moyes' man management has left a huge amount to be desired this season, with reports of disillusionment and unease between several of the club's high-profile stars. Danny Welbeck is the latest to be the subject of reported unrest, whilst Giggs himself reportedly missed a coaching meeting last month with Moyes, claiming it was "pointless, as Moyes doesn't listen".
The story was denied by Giggs, but it seems clear that all was not well within United's coaching set-up. Whilst the player-coach may lack experience, is there any individual other than Sir Alex Ferguson who knows the various personalities within United's dressing room more than the Welshman?
Finally, it looks likely that Giggs will be handed the job on a caretaker basis until the end of the campaign. He effectively has a no-lose audition for one of the biggest jobs in world football. You try getting rid of him should United win all of their remaining games under his control - this is a chance to get skilful feet under the desk.
Louis van Gaal
Van Gaal will have plenty of suitors when he leaves his Holland role after the World Cup, while he has the added advantage of enjoying a close professional relationship with Robin van Persie, an increasingly disconsolate figure at Old Trafford. If any coach can encourage another season of Van Persie brilliance, Van Gaal may be that man.
At 62, Van Gaal may not feel like the 'long-term project' manager United are perhaps seeking, but this is a time at which fires need to be fought, and there are few more suitable candidates than the Dutchman. His roll of honour reads in mightily impressive fashion: seven league titles, seven other domestic trophies, the UEFA Cup, two UEFA Super Cups and the Champions League - all achieved since 1993 and in three different countries.
The only concern may be a failed stint at Bayern Munich that ended in 2011 after finishing third in the Bundesliga, but Van Gaal's record of managing many of Europe's top players over the last two decades speaks for itself - this is by far the most shiny CV on the pile.
Frank de Boer
In many ways, De Boer is exactly what United wanted from one of their own 'golden generation', a player that has seamlessly taken to management like the proverbial Dutch 'eend in het water'.
Ajax seem likely to win their fourth consecutive Eredivisie title this season, all achieved using young players from the club's academy and playing a brand of football United could only dream of at times during Moyes' reign.
Ajax play with a high-pressing 4-3-3 formation that is wonderful to watch, aiming to win the ball high up the field and immediately embark on a quick attack. They typically pass the ball around patiently until a player is considered able to receive the ball and run at the defence, with wingers drifting in-field to exploit gaps. It sounds an awful lot better than cross after cross after cross after cross.
That said, his appointment would still be a substantial risk. He has only ever managed at one club, and Ajax have failed to make any significant impact in European competition. Without being dismissive, does the Dutch league provide enough solid evidence that De Boer can cope with the pressure of the United hot-seat?
Oooh, aren't we being cheeky? Pinching Everton's manager for the second time in a year would certainly be seen as a naughty move, but if United want to recruit a manager with Premier League experience, then Martinez probably comes behind only Jose Mourinho and Brendan Rodgers on the 'yes please' list.
Moreover, this is a manager who knows exactly the requirements of the role. Martinez has experience of taking over from Moyes, transforming Everton into a much more exciting team to watch this season. The Spaniard has also displayed a tactical flexibility so often lacking in Moyes' approach at United; a Plan B that is not only instigated reactively to an ongoing match situation but also proactively in order to gain an advantage over the opposition.
Unlikely, but funnier things have happened. Just don't make a derisory offer for Ross Barkley three weeks after joining, Bobby.
Daniel Storey - Follow him on Twitter.