RUBEN EYES BIGGEST CHALLENGE

HISTORY has a danger of repeating itself and it's transpired at Old Trafford when it comes to replacing iconic football managers. Manchester United have discovered that it's extremely difficult to appoint successors to Sir Matt Busby and Sir Alex Ferguson. Their two legacy managers oversaw 18 of their 20 top-flight titles and three European Cup triumphs in 1968, 1999 and 2008.

- ROBERT J WILSON

In between those two legendary dynasties, the club appointed some prominent managers such as Jose Mourinho, Ron Atkinson, Louis van Gaal and Tommy Docherty, but they were limited to cup successes rather than being serious contenders for league titles.

Busby famously rebuilt the football club following the tragedy of the Munich Air Disaster. A decade on from losing eight of his players and recuperating from his own death bed, Busby triumphantly led Manchester United to their first European Cup success in 1968.

Objective achieved, Busby elected to retire at the end of the following season. The United board promoted from within, with Wilf McGuinness given the opportunity to step up from the reserve team.

The challenge proved too overwhelming and Busby was coaxed back out of retirement in December 1970 to oversee a turbulent season.

In search of a suitable replacement, the club failed in their approaches for Jock Stein and Don Revie, and ended up with Frank O'Farrell. Later, Docherty, Dave Sexton and Atkinson all failed to restore United to the pinnacle. That altered in November 1986 when Ferguson arrived from Aberdeen.

The Scot was awarded enough time to establish his own blueprint and, four years after his appointment, an FA Cup victory over Crystal Palace provided the springboard for what was to come.

That elusive first title since Busby in 1967 finally arrived in 1993 and under Ferguson's 27-year reign a dozen more Premier League titles would follow. His final title victory fittingly came at the end of his final season in 2013.

Like Busby before him, Ferguson has been a difficult act to follow David Moyes was treated appallingly and not given sufficient time to implement his own authority. Barely nine months later, he was replaced by Van Gaal.

Then serial winner Mourinho was considered a better bet in 2016, but the club were by then slipping further behind their arch-rivals Manchester City and Liverpool.