With that avenue closed, Atletico Madrid are weighing other options, and Napoli full-back Mathias Olivera has emerged as a serious possibility.
The 28-year-old Uruguayan has interested Atletico since his days at Getafe, and a potential deal could now develop through an unusual route that may suit several parties simultaneously.
Napoli, with head coach Massimiliano Allegri's approval, are looking for a new right-back and have identified Atletico's Nahuel Molina as a target, a player Allegri previously considered while in charge of Juventus.
According to AS, there is genuine interest in both full-backs from each club, and Italian outlet La Gazzetta dello Sport reports that a swap deal could be structured, even if it is processed formally as two separate transfers. Both players carry a market value in the region of €15m.
Molina has been a regular fixture in Atletico's plans under Diego Simeone, even if the presence of Marcos Llorente has limited his opportunities in recent seasons. The Argentine, who holds a European passport, has remained an important figure for his country under Lionel Scaloni over the past five years despite that competition for his place at club level.
He came close to leaving last summer, with significant offers from English clubs on the table, but ultimately chose to stay, partly because his first child was due to be born and partly because he felt settled at the club and in the city.
Whether this summer brings a different outcome will depend on how Atletico's pursuit of Olivera develops and on Napoli's own willingness to let Molina leave on terms that work for everyone involved.
For Atletico, resolving the left-back position would close out a problem that has resurfaced summer after summer, with a string of options considered and discarded over the years without a long-term solution ever being found.