There's a refrain from fans when a popular footballer wants a new contract: "Pay them what they want." But how far do you take this? What do Manchester United do when negotiating in a market full of bluffs and lies -- beyond building up as much intelligence as possible to make the best decision?

United have the second-highest wage bill in world football. Barcelona, their opponents in the Champions League quarterfinals, have the most expensive -- and they also have the best player in world football, Lionel Messi. Barca's wage bill is now 73 percent of their revenue, a figure the club view as unsustainable and want to cut. Barca players will be sold this summer to achieve that. And that's at Barca, a not-for-profit club owned by members.

At United, there are demands to push the wages up further with several players wanting substantial rises as their contracts run down. They know what the club's top earner, Alexis Sanchez, is on -- £300,000-a-week plus bonuses according to reports -- and they want parity or an even healthier fraction of it. Could you blame them, especially if they're contributing more to the team? And just about every player is contributing more to United than the Chilean who arrived with a fanfare but has been a flop. If United acquiesce to these demands then they'll have the highest wage bill in football, yet would anyone say this United team deserves that rate of pay?

However, this isn't the United of "no value" in the transfer market of a decade ago, when they missed out on £30 million Karim Benzema. They are now big, big payers.

United have money and Ed Woodward has always been bold on the subject of the club being able to pay well. I asked him not long after he'd taken over what would happen if the club had another Cristiano Ronaldo who wanted to leave, and he said: "We won't lose on price."

The implication was that United could match anyone, but that was in 2013. Price matching has now become a potentially reckless action.

That brings us to David De Gea, without question one of the best goalkeepers in the world but with a deal that expires in 15 months. United were able to delay the inevitable contract wrangle by, in November, activating a clause in the Spain international's contract that keeps him at Old Trafford until 2020. But now fresh terms must be agreed.

By paying Sanchez such an inflated wage, it has a knock-on effect as contracts for other star players come up for renewal, and that is certainly the case with De Gea.

United are prepared to make De Gea the best-paid goalkeeper in the world. It's not enough for him and, not only that, his agent's fees have staggered the club. Yet United need to have a good relationship with the top agents who are the gatekeepers to the top talents.

The club are under pressure because, in De Gea's case, he's chosen his own pace at which to negotiate, a decision that made sense given the state United were in at the start of the season under Jose Mourinho.

De Gea can run the contract down and leave for free if he chooses. It's his life, he can have his reasons. If he wants to go back to Spain then he couldn't be blamed, but then United can demand a huge fee this summer, too. And he'd still need those vast wages.

What could United have done differently? De Gea was already the best-paid goalkeeper when he signed his last deal. He sent out positive indications about renewing again but, so far, nothing has been agreed. De Gea's talents aren't in question, nor his professionalism. Look at it coldly: he's signed a contract that he'll honour. And he might sign another if it's big enough. He also knows that it would cost a mighty transfer fee to replace him.

Sanchez didn't have a transfer fee, but nor was he free. Henrikh Mkhitaryan, a £30m player, went the other way.

Manchester City didn't sign Sanchez in 2018 because they felt his wages would smash their pay structure. They were right, but as the incumbent champions of England, they made that decision from a position of strength. They weren't in that position in 2009 when they signed Carlos Tevez. A decade on, Tevez's former United teammates still talk about the amount of money they suspected he was paid by City.

That same chat with Woodward years ago is very revealing, particularly as he now does so few on-the-record interviews.

"Spending an extraordinary amount on a player, that is more than you should on a player, can have negative consequences," he told me. "It can have negative consequences on other players in the team. It also has a knock-on effect on the salaries of the other players. A perception that we overpay is not a good thing either."

It's very easy to look back at transfers with the benefit of hindsight. It's not an exact science and never has been. There have always been flops.

United create their own wealth, proudly so. They don't have the sovereign wealth fund of a state behind them. United do not have billionaire benefactors who can afford to let the club run at a loss. United have never breached financial fair play rules, never had a transfer ban. Mourinho felt United's rivals were cheating the system, yet United's wage bill is vast and it's not punching its weight. Giving players a new contract may please fans, but fans can quickly change their tune.

"You end up focusing on what you think the right answer is," Woodward said. "Equally, you might be faced with some stark decisions: do I pay a relatively large amount of money to an agent or do I lose the player?

"We need to be very thoughtful about which way we go on decisions. We haven't always got every player either. We didn't get Benzema, Lucas Moura or keep Paul Pogba. Sometimes they are difficult decisions to make."

United are faced with such choices now. Clubs don't like admitting this to fans, but they have the right to say no. They have the right to let a deal go to the wire, though they can get it wrong as Arsenal did with Mesut Ozil, who effectively held them to ransom. And even if they call the bluff of the players' demands and decline, that could damage the relationship between club and player. And if they say yes, there will be another wave of players wanting vastly improved contracts.

It's not like those asking for more are treble winners, either.