Transfer journalist Nicolò Schira is reporting the Seville club's concrete interest in the 26-year-old Senegal international.
Dieng's contract at Lorient expires this month, making the operation financially straightforward for Betis — who can acquire a proven Ligue 1 striker at no acquisition cost, a structure that suits a club simultaneously planning for European competition and managing their wage structure responsibly.
The forward scored 11 goals in 33 Ligue 1 appearances for Lorient this season, demonstrating the combination of direct pace, physical presence and finishing ability that Pellegrini is seeking as a complement to the attacking options already at the club.
Dieng made his name in French football after leaving Marseille in 2023 and has consistently produced double-figure goals across his time in Ligue 1. He has 17 senior caps for Senegal.
Whether Betis move first and quickly will matter given that free agents at his level will attract multiple approaches. The signing requires no negotiation over a fee — only agreement on personal terms.