The Spanish side beat Fenerbahce to progress to the last eight but their domestic form has been far less impressive, with Sampaoli unable to improve the club's form after replacing Julen Lopetegui in October.
Sevilla currently sit two points above the relegation zone in 14th place, with a 2-0 defeat at Getafe on Sunday Sampaoli's final game in charge.
Jose Luis Mendilibar set to be appointed by Sevilla ahead of taking training later on Tuesday. Mendilibar's previous job ended last year with a record of one win in 12 games at Alaves.
Sevilla play Cadiz and Celta Vigo in La Liga after the international break before facing United in the first leg of their Europa League quarter-final tie on April 13.
The Liga club are the most successful team in Europa League history, winning the competition six times and most recently in 2019-20.