Unfortunately, 18 months later, it seems the Chilean's transfer has been one of the worst in recent memory.
In one-and-a-half seasons, he's made just 45 appearances, scoring a laughable five goals.
His reward for those disappointing numbers? Over £41 million in the bank.
That's right. Sanchez's ridiculous basic wage of £505,000 per week has seen him break the £41 million mark.
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If you're curious, he's cost Man United £8.2 million per goal.
He's certainly not been a worthwhile investment then. And due to various injuries, the forward has also sat out 20 club fixtures.
It's actually laughable that Sanchez has made so much money, despite doing so little on the pitch.
In fact, it's also been suggested that his huge wage is having a negative effect on the dressing room too.
We've heard plenty of rumours that goalkeeper David de Gea has been demanding a huge new contract to stay at Old Trafford, while other players are trying to cash-in too.
Paulo Dybala was linked with a sensational move to United in the final week of the summer transfer window, but talks stalled over his demands.
He won't be the last player to try and take Ed Woodward for a ride either, such is the culture at Old Trafford since Sanchez's big move.
Thankfully though, it doesn't look like Ole Gunnar Solskjaer or the club will stand for it any longer.
The new transfer policy is said to be moving away from buying big-name superstars and an emphasis will be on blooding youth - as it used to be.
We've seen that with the acquisitions of Daniel James and Aaron Wan-Bissaka this summer, while United's starting XI vs Chelsea was the youngest in the Premier League last weekend.
Their reward for trusting youth? A 4-0 win against a top-four rival. United were winners on Sunday, but with Sanchez taking home £41 million, it seems they're still fighting a losing battle with that one.News Now - Sport News