Talks between the clubs are at an advanced stage for Feddal, 30, to join Sporting when the La Liga season ends.
Sporting will pay a €3m fee for the centre-back, giving Betis a small profit on the €2.5m they paid in 2017.
Feddal joined Betis from fellow Spanish side Alavés and he has gone on to make 59 appearances.
However, Valencia wanted him on loan without an option to buy, a formula that did not satisfy Betis.
Unless of any hitches, Feddal will soon move to Portugal with Sporting and replace the retiring Jeremy Mathieu.
Betis enjoy good relations with Sporting having signed William Carvalho from them two years ago.