The Chilean signed a huge contract worth £500,000-a-week after joining from Arsenal in January 2018.
Alexis has since scored five goals in 45 appearances for United, and Evra thinks he has not given his all for the club.
He told Sky Sports: "Some players only come for the money, I am not afraid to say that.
"I have nothing against him, but Sanchez, when I saw the deal, that's when I thought the Manchester United history just went down.
"He had Manchester City, they were offering less money but he was going to play better football than United - I'm sorry about that, but City play better football and Guardiola will improve him.
"So I want to know what is the real reason for choosing United? Don't tell me he loved Manchester United when he was a kid.
"It's either the money or he wanted to be the number one, take the No 7 shirt and be the star."
Need a VPN? Or seeking to switch? Then support Tribal Football by clicking here to sign up with our official partners NordVPN. Not only will you receive the best VPN experience, but also great discounts by signing up via Tribal Football. Thanks for your support!