United are set to incur a significant financial loss on Antony, who was their second most expensive signing at £85m in 2022.
Antony is travelling to Spain for a medical and to finalise personal terms with Real Betis.
He had a successful loan spell at Betis in the latter half of last season, scoring nine goals in 26 games and helping them reach the Conference League final.
Despite a strong start at United, scoring in his first three Premier League games, his performance declined, with only 12 goals in 96 appearances overall.