Revelling in his new role as one of social media’s unlikeliest influencers, Mike Phelan posted an innocuous Tweet this week.

“Captions please” it read, along with a photo of Manchester United’s assistant mouthing instructions to interim manager Ole Gunnar Solskjaer on the touchline at Old Trafford.

Inviting comments on Twitter is always a risky move. But rather than a stream of invective, Phelan can’t have failed to notice a common thread.

“See Ander? If you let him go, you’re in big trouble,” read one early reply.

“Look Ole, Ander needs a new contract,” read another.

And they continued: “Give Herrera a contract extension”

“You see that Ander Herrera, we mustn’t let him leave”

“Do you see that man over there? Ander Herrera? That’s our lord and saviour.”

There were also liberal mentions of Jadon Sancho and the need to lure him away from Borussia Dortmund at any cost – but in a time of great flux at Old Trafford, Herrera is at the forefront of Man Utd fans’ minds.

And he is becoming a headache for the club’s hierarchy who refuse to be held to ransom over a new deal as Herrera moves ever-closer to becoming a free agent at the end of the season.

The Spaniard is one of the biggest beneficiaries of United’s revival under Solskjaer.

He has become an immoveable figure in the Norwegian’s strongest midfield trio, alongside Paul Pogba and Nemanja Matic.

United’s engine room still isn’t perfect – hence interest in Sporting Lisbon’s Bruno Fernandes and potentially one more midfielder this summer. But Solskjaer has come closer than anyone since Sir Alex Ferguson to getting the blend right in the middle of the pitch.

Herrera has been key to that, doing so much of the dirty work to free up Pogba’s more attacking instincts – and providing the energy often lacking in Matic.

The 29-year-old has come a long way since Jose Mourinho urged United’s board to hand him a new contract on the basis of his off-field influence.

Mourinho accepted Herrera would be a fringe member of his squad going forward – but believed his character was vital to the dressing room.

Entering the final year of his deal, sources close to Herrera privately claimed at the start of the season that the decision over his future would ultimately come down to United. The player had no intention to leave and, as such, links with a return to Athletic Bilbao were promptly dismissed.

But negotiating with a bit-part player, who is just happy to stay where he is, is very different to locking down the future of a key component in one of the most uplifting periods in the club’s recent history.

Herrera has always enjoyed a cult status among fans – now he is producing the performances to fully justify it.

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Those same supporters who berated Louis van Gaal for what they deemed criminal underuse of the terrier-like midfielder, are basking in a sense of vindication.

Ed Woodward, whose populist decision to bring Solskjaer back to Old Trafford, now risks infuriating fans over the delay in resolving Herrera’s future.

Sources say United have been amazed by some of the demands being made by players and agents during their latest rounds of contract negotiations.

The question is whether Herrera can change the minds of their power-brokers amid claims he is looking for in excess of £200,000-a-week.

They were the ones who were happy to let him enter the final 12 months of his contract – and there has never been the sense of urgency over his deal as there was/has been regarding Luke Shaw, Anthony Martial and David de Gea.

The signings of Pogba, Matic and Fred in each of the last three summer windows are evidence of the belief that significant improvement was needed on the club’s roster of midfielders.

In Pictures | 11 famous footballers then and now 11 show all In Pictures | 11 famous footballers then and now 1/11 Lionel Messi for Barcelona 2005 and 2016 2/11 Cristiano Ronaldo for Manchester Unted 2003 and Juventus 2019 3/11 Gareth Bale for Wales 2018 and 2006 4/11 Neymar for Santos 2009 and Paris Saint-Germain 2019 5/11 Andres Iniesta for Spain 2003 and 2018 6/11 Sergio Aguero for Manchester City 2019 and Argentina 2006 7/11 Aaron Ramsey for Arsenal 2008 and 2019 8/11 Mesut Ozil for Germany 2006 and 2018 9/11 Paul Pogba for Manchester 2009 and 2019 Man Utd via Getty Images 10/11 Wayne Rooney for DC United 2019 and Everton 2002 11/11 Zlatan Ibrahimovic for Los Angeles Galaxy 2018 and Ajax 2002 1/11 Lionel Messi for Barcelona 2005 and 2016 2/11 Cristiano Ronaldo for Manchester Unted 2003 and Juventus 2019 3/11 Gareth Bale for Wales 2018 and 2006 4/11 Neymar for Santos 2009 and Paris Saint-Germain 2019 5/11 Andres Iniesta for Spain 2003 and 2018 6/11 Sergio Aguero for Manchester City 2019 and Argentina 2006 7/11 Aaron Ramsey for Arsenal 2008 and 2019 8/11 Mesut Ozil for Germany 2006 and 2018 9/11 Paul Pogba for Manchester 2009 and 2019 Man Utd via Getty Images 10/11 Wayne Rooney for DC United 2019 and Everton 2002 11/11 Zlatan Ibrahimovic for Los Angeles Galaxy 2018 and Ajax 2002

Fernandes could cost as much as £90m if Sporting insist on their captain’s buyout clause being met.

Should the free-scoring 24-year-old arrive in the summer, where would that leave Herrera?

Likewise if Fred overcomes a woeful start to life in the Premier League and lives up to the potential that saw United make the £52m Brazilian the fourth most expensive signing in their history.

Herrera turns 30 at the start of next season – and with a contract of £200,000-a-week or more, becomes virtually unsellable.

United are paying the price for allowing the situation to reach this point. And the flawed policy of using 12-month options as a negotiating safety net will surely be one of the first issues addressed by the incoming director of football.

But the pressing concern right now is how much it would cost to replace Herrera in the current market if he’s allowed to walk away for nothing.

He may be in the unique position of being a player they can’t afford to keep – but can’t afford to let go either.