De Fanti was appointed at the Stadium of Light in June last year, spearheading a recruitment drive that saw Sunderland sign 14 players in the close-season.
However, the likes of Modibo Diakite, Valentin Roberge and Jozy Altidore have all struggling to adapt to life in the Premier League, while midfielder Cabral has been sent on loan to Genoa after making just two appearances following his move from Basel.
Poyet's side also hold a 2-1 lead going into the second leg of their League Cup semi-final with Manchester United.
Sunderland's last signing of De Fanti's reign came earlier this month with the capture of defender Marcos Alonso on loan from Fiorentina.
A statement on the club's official website read: "Sunderland AFC has announced that the club has parted company with Director of Football Roberto De Fanti.
"The club would like to place on record its thanks to Roberto and wishes him well for the future."
