Ferguson, 76, was rushed to hospital yesterday for emergency surgery on a brain haemorrhage.
The ex-Red Devils boss is seriously ill and is now in intensive care.
Messages of support have flooded in from around the globe for the most successful manager in British football history.
And last night Brazilian midfielder Anderson, 30, left his Instagram followers crying after he posted a picture of himself high-fiving the Scot.
He said: "Boss, I learn with you to win whatever happens, so now I demand you: win, win, win, win. Please.
"You are the best I have ever known, as a person, as a manager. Can't wait to see you again.
"My best wishes boss. Get well soon. Please."
The post sparked an emotional response from some of his 186,000 followers.
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One said: "That really hit a soft spot there."
Another added: "So touching, keep strong for him Anderson."
A fellow person on social media said "my heart's breaking" along with a crying emoji.
And one fan said: "Wow, I'm going to cry."
Earlier today star boxer Tony Bellew, 35, was praised for his message of support for Ferguson just hours after he secured a stunning 5th round TKO over British rival David Haye, 37.
He said on Twitter: "Thoughts are with the legendary Sir Alex Ferguson right now.
"Hearing he's in hospital so hope he's okay.
"The greatest manager I've ever seen. #GetWellSirAlex."