Club Bruges emerged as a candidate for the 19-year-old, who has not made his first team debut for United since arriving from Penarol last summer.
Pellistri is said to have advocated a move to Spain, with Alaves recently named as the favorite to sign a six-month loan deal with the Uruguayan.
A deal has now been made with the La Liga club and the teen will travel to Spain over the weekend for one, according to the Manchester Evening News Complete move.
Pellistri has scored three goals at U21 and U23 for United but was recently unavailable for selection due to a positive coronavirus test.
Alaves are currently 18th in the La Liga table before meeting Getafe at the weekend.
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