The Eagles identified the 28-year-old Ecuadorian as their preferred option to strengthen the left flank late in the window, with Portuguese outlet Record reporting that Benfica made several attempts to sign him during the final weeks of August. Those efforts, though, went nowhere.
Manager Ruben Amorim was the man who blocked the move, choosing to keep Estupinan in his squad for the 2026-27 season rather than sanction a sale. Aston Villa had also been tracking the player for some time and appeared close to a deal earlier in the summer, only for Amorim to insist he wanted to assess Estupinan in preseason before deciding on his future.
With the move to Lisbon off the table, Benfica turned elsewhere for defensive reinforcements, ultimately signing Souffian El Karouani on loan with an option to buy from Al-Qadisiya.
Estupinan, meanwhile, remains at San Siro, where he joined from Brighton for an initial €17m plus bonuses last year and has struggled at times to fully win over the club's management, despite scoring the winner in last season's derby against Inter.
The Ecuadorian's future had appeared genuinely uncertain for much of the summer. AC Milan had been willing to let him leave after a mixed first season, with head coach Massimiliano Allegri at times preferring the younger Davide Bartesaghi in his place.
Aston Villa's interest was reported to be the most concrete, and a switch to the Premier League appeared possible before Amorim's intervention closed off that route as well.
Estupinan, who has also represented Osasuna, Mallorca, Almeria, Granada and Villarreal during a career largely built in Spain, will now look to fight for a regular starting role at Milan under Amorim this season, with his long-term future at the club still far from settled despite surviving the summer window.