Five potential successors to David Moyes
Atletico Madrid's Argentinian coach Diego Simeone looks on during a press conference at the Vicente Calderon stadium in Madrid on April 21, 2014 - by Javier Soriano
Below, AFP Sports looks at five potential contenders to replace the Scot in one of the most high-profile jobs in world football.
Diego Simeone (ARG)
Has impressed while guiding Atletico Madrid to the Champions League semi-finals and to the top of La Liga, challenging the dominance of Real Madrid and Barcelona at the summit of Spanish football. The former Argentina midfielder remains best known in England for being the player David Beckham kicked to be sent off during a last 16 match at the 1998 World Cup in France; a game England eventually lost.
Louis van Gaal (NED)
The Netherlands manager is one of the most experienced coaches in world football, having been in charge of a host of major clubs including Ajax, whom he guided to Champions League glory in 1995, Barcelona, AZ Alkmaar and Bayern Munich. Has made no secret of his desire to work in the Premier League, but his role with the Dutch side at this year's World Cup in Brazil could reduce the time he has to bring in new players to Old Trafford during the close-season transfer window.
Jurgen Klopp (GER)
The charismatic 46-year-old has enjoyed great success while in charge of Borussia Dortmund, guiding an effervescent, hard-working team to back-to-back German league titles in 2011 and 2012, plus last season's Champions League final. However, they are currently a distant second in the Bundesliga table behind already-crowned champions Bayern Munich. Has also been linked with the manager's position at Barcelona.
Ryan Giggs (WAL)
The most decorated player in English football history and United's record appearance holder, the ageless Welsh midfielder is currently on the staff at Old Trafford as a player-coach. Whether the 40-year-old has the experience and strength of character to be more than a stop-gap appointment is an open question, but he would certainly be a fans' favourite.
Alex Ferguson (SCO)
The former United boss, British football's most successful manager, has insisted that there is no way he would return to the hot-seat following his retirement at the end of last season. But is the 72-year-old Scot, now a United director, really content to stay on the sidelines while his work of more than 26 years unravels in front of his eyes? May feel pricked by responsibility as Moyes was hired on his recommendation.