The four-year deal will see Díaz, who turns 22 in January and is contracted to Atlético until 2028, join up with his new Sevilla teammates in time for their pre-season training camp in the Netherlands, which gets under way on Thursday. With the transfer edging closer, Diego Simeone left him out of Monday's session entirely; rather than train on the pitch, Díaz worked in the gym so as not to risk picking up any knock that could complicate the move.
Born in San Fernando de Henares and a product of Atlético's academy since childhood, Díaz can also play on the wing and has amassed around 30 caps across Spain's various youth national teams. He made his first-team debut under Simeone last season, starting all four of his Primera División appearances for a total of 311 minutes, including a league fixture away at Sevilla's own Sánchez Pizjuán.
Atletico Madrid had also been negotiating with Levante over Díaz in recent weeks and reportedly had an initial agreement in place, but the player ultimately chose Sevilla's project. By retaining half of his federative rights, Atlético keeps a stake in any future sale, a formula the club has increasingly applied to promising academy graduates who move on for regular first-team football.
Arnau Solà, a 23-year-old left-back who joined on loan from Portuguese side Arouca after coming through Barcelona's La Masía academy, has already stepped into Díaz's place in Atlético Madrileño training sessions, meaning Simeone's first-team squad numbers at left-back are unaffected regardless of when Díaz's exit is formally confirmed.
The move continues a pattern at Atlético of selling highly-rated youth players to Primera and Segunda División clubs once first-team opportunities become limited under Fernando Torres' reserve side, while the parent club retains buy-back options or a percentage of future transfer fees. An official announcement from both clubs is expected once the remaining details of the deal are finalised.