Manchester United are on red alert after being given fresh encouragement in their long-standing pursuit of Real Madrid forward Gareth Bale.

Bale has been coveted by United for years, with the club first trying to sign the Welshman in 2007 before he joined Spurs and then failing with a £103 million bid to hijack his move to Real four years ago.

But United could be about to make a fresh move for Bale after Zinedine Zidane admitted he could not guarantee the 28-year-old will remain at the Bernabeu this summer.

Real are hoping to sign France striker Kylian Mbappe from Monaco in a potential £161 million world record deal that has intensified talk of one of the club’s prominent array of forwards making way. Questions have also been raised about the futures of Karim Benzema and Cristiano Ronaldo this summer but Bale is seen as the most expendable of that trio following his battles with injury and struggles to dislodge playmaker Isco from the team.

There is also thought to be a belief that the European champions, who have brought in around £90 million in sales this summer, need to raise more capital to help fund the move for Mbappe.

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United have held talks with Inter Milan over Croatia winger Ivan Perisic as manager Jose Mourinho targets two more signings although they have decided not to compete with Paris St Germain for Barcelona striker Neymar nor will they join Manchester City in the race to sign Arsenal's Alexis Sanchez.

Serbia midfielder Nemanja Matic seems likely to join from Chelsea but a high quality winger is Mourinho’s priority and Bale would provide an injection of star quality that the Portuguese has admitted his team lack and Zidane’s remarks could embolden United.

Asked about the prospect of one of his leading forwards leaving this summer, Zidane could offer no guarantees. “I hope they all stay for this season,” the Real coach said. “I hope everyone remains. I want everyone who is here now to stay, but anything can happen right up until August 31.”

Pressed on the subject of Mbappe and the ramifications that could have for the likes of Bale, Zidane added: "I'm the coach, you need to speak with someone else about whether or not it's worth it. Nothing has happened until now, and we have the squad we have."

United have bene linked with Ivan Perisic

United lost 1-0 to Barcelona courtesy of Neymar’s first half goal at FedEx Field in Washington DC in the early hours of Thursday.

And despite Barcelona coach Ernesto Valverde claiming Manchester United can win the Champions League next season and that he would not want to face them in the competition, Mourinho admitted his team are not at the level of the Catalan giants or Real.

Mourinho said that, with the exception of midfielder Paul Pogba, United did not have the players to rival the likes of Neymar, Lionel Messi or Luis Suarez at Barcelona or Ronaldo and Bale at Real, whom United beat on penalties in Santa Clara last Sunday when Mourinho embraced Bale warmly.

And while the United manager said such talents can be countered by a "certain tactical organisation", he claimed their superior quality often wins out.

Kylian Mbappe is expected to join Real Madrid

"I think in this moment the best players are at these two clubs (Barcelona and Real) and you have to accept that as a reality but for us to play against both in pre-season without any kind of pressure, or being worried about the result, was very good for us," Mourinho said.

"There is only one Messi and one Neymar, one Suarez, Iniesta, Pique, Ronaldo, Bale, Modric, Toni Kroos. There is only one (of each) so they can only be playing for one club not two.

"We can't have them, they belong to those clubs. You can work very hard tactically to improve your players but there are players that are special players and there is nothing you can do.

"You try to compensate for the difference in quality with a certain tactical organisation and with that you can win in football. It's possible a team is, on a certain day, better than the sum of its parts.

"But their parts are amazing, their relation with the ball is amazing. You can argue about the occupation of spaces but the relation with the ball is still the most important thing and as an opponent on the bench, like I am, it is beautiful to see their relation with the ball.

"But one of my players, Paul Pogba, showed he belongs to that level."