Memphis Depay was given permission by Barcelona to train with Atletico Madrid on Thursday as the teams negotiate a transfer.
Netherlands international Depay has struggled for playing time at Barca under Xavi and his contract ends at the end of the season.
Widespread reports this week suggested Atleti are prepared to pay an initial €3million for Depay, potentially rising to €4m with add-ons.
While a deal has yet to be struck between the clubs, Atleti have confirmed talks are at an advanced stage, with Depay now training alongside his soon-to-be team-mates.
"Memphis, with permission from Barcelona, trained for the first time in Majadahonda while both clubs close their transfer," Atleti posted on their official Twitter page.
Depay joined Barcelona on a free transfer from Lyon ahead of the 2021-22 season, linking up again with Ronald Koeman, for whom he had played for with the Netherlands.
But Koeman was fired by the Blaugrana in October 2021 and his successor Xavi never appeared to have the same trust in the former Manchester United and PSV attacker.
Depay's first 11 LaLiga appearances were all as a starter, but after Xavi's appointment only nine of his next 17 top-flight outings came from the start.
He is set to become fourth-placed Atletico's first signing of a January window that has so far seen Joao Felix leave for Chelsea on loan and Matheus Cunha join Wolves.
Should the deal go through in time, Depay could make his debut against Real Valladolid on Saturday.