Who will fill Fergie's boots?

Manchester United manager Sir Alex Ferguson's shock decision to retire at the end of the season has sparked intense speculation over who will claim the Old Trafford throne.

Here are some of the leading candidates for arguably the biggest job in world soccer:

Jose Mourinho

The charismatic Portuguese introduced himself with his famous jig down the touchline when his Porto side knocked United out of the Champions League in 2004 on the way to winning the tournament.

He won two league titles at Chelsea, and since leaving Stamford Bridge in 2007 he has won league titles in Italy (Inter Milan) and Spain (Real Madrid).

He also claimed the European Cup for Inter and is desperate to achieve the feat in a third country.

David Moyes

The third-longest serving manager in England's top flight after Ferguson and Arsene Wenger, Moyes has a shrewd tactical ability and strong work ethic. Thanks to him, Everton compete near the upper reaches of the league despite a relatively small budget.

Juergen Klopp

The 45-year-old coach of Borussia Dortmund has proved himself in the Bundesliga since taking over in 2008.

He steered Dortmund to a first domestic double last year and though Bayern Munich have won the title this season by a large distance, his stock rose further after the club's win over Real Madrid in the Champions League semi-finals.

He recently said he wanted Dortmund to "play football that people remember", and that would sit well with the United hierarchy.

Ole Gunnar Solskjaer

The Norwegian has been well-tutored in Ferguson's management skills, having coached the reserves after hanging up his boots.

Now at his boyhood club Molde, which he took to consecutive Norwegian titles, the 40-year-old is still highly-regarded at United, with Ferguson last year tipping him as his eventual successor.

Michael Laudrup

An outsider, maybe, but the Dane is turning heads with his work at Swansea City,winning the League Cup this season, the club's first major trophy. One of the most skilled players of his generation, Laudrup preaches attractive passing football and his Swansea side have been one of the most pleasing on the eye this season.

Ryan Giggs/Gary Neville

Welsh winger Giggs was discovered by Ferguson as a teenager and has gone on to become one of the club's greats, with more than 900 appearances and counting.

Giggs is already preparing himself for life after playing by taking his coaching badges, but it is highly unlikely that he would be thrust into the top job so soon.

However, he and his old team-mate Neville could form a future "dream team" alongside an older coach such as Moyes or Martin O'Neill.