Who can take over hot seat?
LOUIS VAN GAAL (HOLLAND)
The Holland 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.
DIEGO SIMEONE (ARGENTINA)
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.
RYAN GIGGS (WALES)
The most decorated player in English football history and United's record appearance holder. 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 the fans' favourite.
He has insisted that there is no way he would return following his retirement. But is the 72-year-old Scot really content to stay on the sidelines while his work of more than 26 years unravels in front of his eyes? - AFP.