The Chilean will arrive in Italy on Tuesday ahead of a loan move with a view to a permanent deal, says Sky Italia.
Inter will pay half of his £505,000-a-week wage packet and can sign him for £14million next summer.
It will mean United will still need to fork out over £250,000 every week despite him playing in Serie A.
Sanchez, 30, has been eager to make the switch across Europe this month having endured a disastrous time in Manchester since moving in January 2018.
He has scored just five goals in 45 appearances for the Red Devils since his move from Arsenal.
Boss Ole Gunnar Solskjaer does not eye Sanchez as part of his first-team plans and was eager to get rid if they received an acceptable offer.