The experienced Argentine left-back, currently at Olympique Lyonnais, had been in advanced talks with the Spanish club. Reports indicated that Tagliafico had given his approval and prioritised a move to Atlético, even speaking with head coach Diego Simeone. He was prepared to accept a squad role at the Metropolitano.
However, the transfer broke down due to financial and squad-registration constraints at Atlético. The club needed to free up sufficient salary space and roster places by offloading other players. While some departures were completed late in the window, not enough room was created in time to finalise the signing.
Tagliafico, a 2022 World Cup winner with Argentina who also featured prominently in the recent tournament, remains under contract at Lyon until June 2027. The defender had attracted interest from other clubs, including Juventus, but shifted his focus once Atlético entered the race.
The collapse leaves Atlético without a late reinforcement at left-back. Lyon, meanwhile, retain the services of the veteran after a chaotic deadline day that saw other potential outgoings also fail to materialise.
At 34, Tagliafico continues to offer experience and leadership. He will now remain in Ligue 1 for the coming season, with any fresh opportunities likely to be revisited in the January window.
The failed move marks another late drama in a busy transfer deadline across Europe, with both clubs forced to adjust their plans after the agreement could not be completed.