And the Mirror say the Red Devils will hand him a huge salary worth a huge £400,000 a week.
Arsenal players now expect an announcement in the next few days.
And United legend Andy Cole thinks the potential arrival of Sanchez would be huge for Mourinho's side.
"If Manchester United bought Sanchez it would be a major-major signing," he said.
Alan Brazil: Alexis Sanchez should join Man Utd
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"We all know what he did at Arsenal, Barcelona and before that Udinese. We appreciate what a good player he is.
"He'll have the choice of a lot of clubs and, if United could get him, it would be a massive signing."
Sanchez is likely to provide foil for Romelu Lukaku at the spearhead of United's attack.
And he will be the first Arsenal player to move to United since Robin van Persie in 2012.