Its is fair to say that many Manchester United fans took for granted the trophy-laden years they had under Sir Alex Ferguson.

The Scot's 27-year reign - between 1986 and 2013 - saw the Red Devils win 13 Premier League titles, five FA Cups, four League Cups and two Champions League titles.

Since his retirement six years ago, United have understandably struggled to replace Ferguson. Not only has this meant that United have won just three trophies since his departure, but the search to find the perfect successor has proved rather expensive.

Three managers have come and gone since Sir Alex's departure - David Moyes, Louis van Gaal and Jose Mourinho - with a plethora of playing styles and philosophies falling on deaf ears at the club.

Moyes was the immediate successor, after his impressively consistent 12 years at Everton led to Ferguson actually picked him to take over, in what undoubtedly added more pressure.

Just nine months into his reign - with United sitting at an uncharacteristically low position of seventh in the league - Moyes was relieved of his duties.

Due to the size of David Moyes' contract - a six-year deal - United had to fork out £5.2 million to pay off the rest of his contract.

Shortly afterwards, Dutchman Louis van Gaal was next up to try and add to his impressive CV at European level.

Van Gaal's last game actually brought his only trophy win for the club, United narrowly dispatched Crystal Palace, 2-1, to win the FA Cup in 2016.

However, the rumour mill had been swirling that Ed Woodward had already chosen his next manager of United, and that was Jose Mourinho.

Despite winning leagues in three different countries and a Champions League with Ajax, van Gaal's slow, possession-based style of play quickly became a permanent fixture of frustration amongst the United faithful.

The Dutchman did last longer than Moyes - two years - but still had a year left on his contract meaning that, once again, United had to empty their pockets. This time around, £8.4 million was enough to complete his departure.

Failing to deliver Champions League qualification in his second season, was arguably the main reason behind the decision.

Then the most expensive departure of them all happened.

Mourinho, who had been linked with the job countless times, finally made the move in 2016 and failed to live up to his reputation.

The Portuguese eventually fell out with a plethora of United players - we would be lying if we said it hasn't happened before - most notably Paul Pogba, and this spelled the end of his reign.

Mourinho did win a Europa League and a League Cup as boss, but will probably be most remembered for signing a rather lucrative contract in January 2018, keeping him at the club until 2020.

Or should I say, increased the amount United had to pay the 'Special One' when he was let go just 11 months later.

Manchester Evening News reported that the figure was as high as £19.2 million for Mourinho and his staff, with Mourinho collecting £15 million of that sum.

Therefore in the last six years, Manchester United have spent no less than £33.2 million on sacking managers since Ferguson left.

It makes you wonder the lengths that the United board and owners will go to in order to restore United's trophy-winning mentality.