Nagelsmann, whose sacking in March 2023 led to Tuchel's arrival, was tipped to return to Bayern, but has now extended his contract with Germany until 2026
A statement from the La Liga champions said they had exercised a buy-back clause in the player's contract for four million euros, less than two months after Eibar had agreed to sign him on a permanent basis for two million euros.
Cucurella, who can play on the left side of defence and on the left wing, came through Barca's youth ranks but only played seven minutes of first-team football in the Copa del Rey before moving to Eibar on loan last season, playing 31 La Liga games.
He made his name with a stunning performance in the Basque team's 3-0 win over Real Madrid and scored against Barca in a 2-2 draw on the final day of the season.