If there was anyone who Manchester United fans didn't want to be announced as Real Madrid's next manager, it was the man who is spending all summer with David De Gea in Russia. Many would have even preferred to see Jose Mourinho return to the Bernabeu than the current Spain coach, Julen Lopetegui, who will be in De Gea's ear trying to convince him to join him in Madrid.

During his playing career, Lopetegui was also a goalkeeper and spent three seasons at Real Madrid, so he has plenty of experience of what he will be offering to the United man.

Five years ago, De Gea won the European Under-21 Championships under the guidance of Lopetegui, who claimed the goalkeeper was "sensational" after his man-of-the-match performance in the semifinal. De Gea was full of praise for his manager back then, claiming that his knowledge as not only a former player, but a goalkeeper too, was a "big help".

They will both be hoping for repeated success in this summer's World Cup, and while they will be concentrating on the tournament, it would be foolish to think that Lopetegui won't be laying the groundwork to convince the world's top goalkeeper to make the journey with him to Real Madrid. After a mistake in a friendly against Switzerland in the lead up to Russia, Lopetegui publicly spoke in defence of De Gea, suggesting that he has already started grafting.

Managers know well that their time at the Spanish giants can be limited, with the first signs of an inability to win the top honours resulting in them being shown the door. If Lopetegui had De Gea as his No. 1, the foundations for success would already be in place.

Every summer, United have the fear of losing their goalkeeper hanging over their heads, with rumours of Real Madrid arising every time the transfer window opens. He has been invaluable to them since signing from Atletico Madrid in 2011, and his contribution to the team has been unrivalled.

No goalkeeper had been named the Sir Matt Busby player of the year before, yet De Gea has won the award in four of the past five seasons, more than any player since it began 30 years ago.

While this is recognition of how well he has played in the past few years, it is also a worrying reminder of the situation the club has been in since Sir Alex Ferguson's retirement. United have grown dependent on him. Gone are the days when a superstar forward was winning them games every week; rather De Gea's world-class saves have seen them pick up three points when otherwise they might have finished the match with none.

Could the pull of new manager Julen Lopetegui finally be enough to lure David De Gea out of Manchester United and to Real Madrid? TF-Images/Getty Images

The sad thing is, United supporters couldn't even really begrudge De Gea's decision if he wanted to leave. Had he signed for Real Madrid earlier, he could have swapped those four player of the year awards for four Champions League titles. United have been lucky to hold on to him for as long as they have.

The club got two or three top seasons out of Cristiano Ronaldo before he traded Manchester for Madrid. The £80 million transfer fee, which was a world record at the time, could go down as one of the biggest bargains given all he has helped them achieve since.

When De Gea first signed as a skinny teenager, there were worries even then that United fans might not see his best years at Old Trafford, just like Ronaldo, with the pull of Real Madrid and his home city too much to ignore.

The goalkeeper will turn 28 this season, and it's hard to believe he won't be eyeing up more top honours while he's still the best. To play for a manager he knows well, who he has experienced success with, has to be appealing. De Gea has won the Premier League, the FA Cup, the League Cup and the Europa League at United, but the days when the club are back to their best hardly appear to be on the horizon.

A dodgy fax machine or an outdated version of Windows, or whatever else it was, denied De Gea the chance to sign for Real Madrid back in 2015. The goalkeeper behaved admirably in response and signed a new deal, which will expire next summer with the option of a further year. He has never been the sort to make ambiguous statements to the press, rather showing true professionalism and only ever talking of his commitment to the club.

It's as if the clock has been rewound and United are back in the same situation as they were three years ago. They run the risk of losing him for free or at a huge discount if they don't sell him soon, as the chances of tying him down to another lengthy contract may be slim. There seems something fairly inevitable about De Gea one day playing in the Spanish capital again, but supporters will be desperately hoping to cling on to him for as long as possible.

"One more year!" they chanted on repeat at Edwin Van der Sar in his final game at Old Trafford at the end of the 2010-11 season. If they were given the opportunity to say the same to De Gea now, they'd sing it until their throats were raw. They know all too well that losing him would make it almost impossible to better their second-place finish of last season.

It's hard to imagine what the club could offer him that would make him extend his stay, though. A better-paid contract? The captaincy? The promise of world-class signings? De Gea doesn't come across as the sort of player who would be swayed by the former two options, but the last one may have an impact.

De Gea deserves to win the biggest trophies, and United have to do everything in their power to ensure he stays so they can bring those trophies back to Old Trafford. The chances of them managing that without him, in the near future at least, are slim. United must act now and do all they can to counterbalance the promises of Lopetegui.