Anthony Martial could become Manchester United's Kevin De Bruyne

Back in 2015, £36 million was actually an astronomical fee to splash out on an unknown 19-year-old prodigy. United fans balked when they learned that the fee could rise to a potential £58 million, and rival fans were having a field day.

But an extraordinary start to his career, an incredible solo goal against Liverpool at Stretford End cemented Anthony Martial as a fan favourite at the Theatre of Dreams. Three years later, his career in England is hanging on by the finest of margins.

Van Gaal's tenure at Old Trafford still has a bitter aftertaste for most United fans, in spite of the fact that he broke their trophy drought with the FA Cup in 2016. Martial, though, was one of his best signings at the club, and the Frenchman's inability to nail down a starting spot under Mourinho has been baffling.

Rumours about his departure were inevitable after another season was spent playing second fiddle (this time to Alexis Sanchez). Perhaps what is most disappointing, is the fact that United's domestic season got off to an electrifying start with 4-0 wins over West Ham and Swansea, with Martial playing a starring role in both.

The downward spiral that followed was only too familiar to fans who have become accustomed to failures in recent seasons. The need for a traditional right winger was apparent, and yet Mourinho chose to bring in Sanchez, a player who had evolved into one of the most devastating left-wingers at Arsenal, in spite of having two perfectly viable options there in Martial and Rashford.

The move eventually cost the Frenchman a place in the national team's squad for the World Cup, which will now be even more painful after his country's successful campaign in Russia. Whispers of a move to Bayern or Chelsea have been annoyingly persistent, but fans have held out hope so far in the belief that United are traditionally not a selling club.

But Martial's sudden departure from the club's pre-season training camp in the US, right before the match against AC Milan, has raised some eyebrows (despite the perfectly legitimate reason of his child's birth).

With Mourinho's own negativity seeping into squad members, inadequate transfer activity, and some question marks over the future of one of their best players, the mood in the United camp could not possibly be worse ahead of the opening week game against Leicester. The fact that Chelsea wants Martial to replace Hazard, and Bayern to replace Ribery and Robben, is proof of his extraordinary potential.

Its sometimes easy to forget that he's only 22, which is all the more reason for Mourinho to keep a hold of him. But the Portuguese boss has made such mistakes before, which will be the biggest point of concern for fans. De Bruyne, Salah, and Lukaku were prematurely sold at Chelsea, and they are now three of the best attacking talents in the Premier League.

While Jose personally might not be feeling the implications now, Chelsea most certainly are. The Blues are still in the market for a world class striker. Hazard is in danger of leaving, which means they need a winger, and Fabregas, their chief midfield creator, turned 31 recently.

Unless United's high brass fight tooth and nail to keep Martial at the club, they will be facing the same situation down the road. With Sanchez also turning 30, it will be in Mourinho's best interests to reject Chelsea and Bayern, even if leaving Manchester would mean regular playing time for Martial himself.

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