Diomande is under contract with Sporting until the summer of 2030, and has previously attracted interest from clubs including Paris Saint-Germain, Chelsea, Manchester United and Liverpool. It was reported on Tuesday that transfer expert Fabrizio Romano understood Nottingham Forest to be in advanced negotiations with Sporting over a move.
Transfer journalist Nicolo Schira has since gone further, reporting that Forest have reached an agreement in principle with Diomande himself over personal terms, with the defender set to sign a contract running until the summer of 2031 should the move go through. The two clubs are said to be in advanced talks over a transfer fee in the region of €38-40million.
Diomande began his career at Danish club FC Midtjylland before making the move to Sporting, where he has gone on to make over 130 appearances and helped the club win two Primeira Liga titles as well as the Taca de Portugal. He is also an established international for Ivory Coast, having been part of the squad that won the 2023 Africa Cup of Nations.
Nottingham Forest's pursuit of Diomande comes as the club looks to strengthen its defensive options following a difficult 2025-26 campaign, with manager Oliver Glasner having previously tried to sign the centre-back while in charge of Crystal Palace.
Should the move be completed at the reported fee, it would represent a significant discount on the €80million release clause included in Diomande's most recent contract extension at Sporting, underlining how far the two parties have had to move to find common ground on a valuation.
Glasner's long-standing admiration for the Ivorian is understood to have been a driving factor behind Forest's revived interest, with the head coach keen to add a proven, physically imposing defender capable of stepping straight into regular Premier League football.
The club's business is also likely to be shaped by developments elsewhere in their squad, with the futures of existing centre-backs Murillo and Nikola Milenkovic both still to be resolved this summer.