Alexis Sanchez's decline at Manchester United over the past 18 months is a complete mystery.

Signed from Arsenal in a swap deal for Henrikh Mkhitaryan, the Chilean was expected to fire Manchester United to glory under Jose Mourinho.

From the piano announcement to the contract worth £500,000-per-week, it really seemed like United had pulled off an incredible signing.

But what's happened since then has been anything but "incredible".

Sanchez, who was almost unstoppable at times for Arsenal, has only scored three  goals in 32 appearances for United, plus six assists.

He's been absolutely awful and now Ole Gunnar Solskjaer is looking to send the 30-year-old and his ludicrous salary on loan to Inter Milan, where Romelu Lukaku resides.

No one saw Sanchez's decline coming and what makes it even worse is that Arsenal had the chance to sign Raheem Sterling in a swap deal for him back in 2017.

No, really.

Manchester City and Pep Guardiola were desperate to sign Sanchez as he entered the final year of his contract, but Arsenal were adamant that they wouldn't sell.

Aware that they needed to sweeten the deal, City offered Sterling as a makeweight in one of their bids. This was according to the Telegraph.

In the end Arsenal said no and both Sanchez and Sterling stayed put. Fast forward to now and Sanchez is a United flop and Sterling is one of the best players in the Premier League.

Classic Arsenal making a wrong decision in the transfer window.

Time is running out for United to get Sanchez out of the club and the latest reports on the saga suggest it may not even happen.

Anthony Martial's injury against Crystal Palace over the weekend could see him ruled out for a couple of weeks, which would leave United short in the wide positions.

What a mess this is becoming.