Paul Pogba is the poster boy of Manchester United's grim decline

Think of the overspending and under-achievement at Manchester United in the last decade - the fantasy, the folly and the systemic failure - and it's hard to come up with a better symbol than Paul Pogba.

Pogba is the personification of what has gone wrong at Old Trafford since Sir Alex Ferguson retired in 2013, even though it would be grossly unfair to put all of United's problems at his feet.

Alexis Sanchez ran him close. Then there were other big-name flops like Angel di Maria, Bastian Schweinsteiger and Radamel Falcao. But when we look back and judge this painful period in United's history, Pogba will be the one who best sums up how it all went wrong.

Ferguson was prepared, albeit reluctantly, to let Pogba leave for next to nothing rather than bow to the demands of the young Frenchman and his agent, the late Mino Raiola.

The new United hierarchy took a different view, taking pride in the fact they broke the world record to re-sign Pogba from Juventus in a deal that also earned Raiola £40million.

It was trumpeted by a social media campaign with the hashtag #pogback and a video posted by the player's sponsor adidas with a soundtrack by rapper Stormzy - the kind of things Ferguson would have detested.

Fast forward six years and the announcement on Wednesday of Pogba's departure as a free agent at the end of the month was rather more muted.

'Once a red, always a red,' was the message from United even though, in Pogba's case, that feels rather hollow.

Pogba replied: 'I feel privileged to have played for this club. Many beautiful moments and memories but most importantly an unconditional support from the fans. Thank you.'

Unconditional support? By the time the Frenchman made his final appearance against Norwich City at Old Trafford in April, the fans' patience had worn so thin that chants of 'f**k off Pogba' rang around the stadium when he was substituted in the second half.

His last game came three days later at Anfield when he limped off inside 10 minutes with United already a goal down and heading for a 4-0 defeat. Too often Pogba went missing when his team needed him the most.

His best season was undoubtedly his first when a partnership with Zlatan Ibrahimovic helped United win their last silverware in 2017, the League Cup and Europa League when Pogba scored against Ajax in the final.

United posted a video of that goal on Wednesday but there are far too few highlights from his six years back at Old Trafford to justify the eye-watering expense and massive expectation.

His relationship with Jose Mourinho turned toxic, and even though he got on better with Ole Gunnar Solskjaer the performances for United didn't improve.

There was also the tiresome public flirtation with Real Madrid and the prolonged injury absences as Pogba popped up in Dubai and Miami while rehabilitating.

The frustration for United and their fans was that there was a world-beater somewhere inside Pogba: a player who won the World Cup with France and four Serie A titles for Juventus.

But United couldn't get the best out of the midfielder under three different managers even though they exercised the option to extend his contract into a sixth year and were open to offering him a new one.

It has been clear for some time that a parting of the ways is in the best interests of the player and the club, although confirmation that Jesse Lingard will also be leaving as a free agent on June 30 means that United will be losing two members of their 2011 FA Youth Cup-winning team at the same time. For a club so proud of its academy system, that is not insignificant.

They won't be the only players to go this summer as part of a major overhaul under new manager Erik ten Hag.

There are a busy few months of transfer business ahead and as United prepare to spend again, you can only hope they have learned from the lesson of Paul Pogba.