Alves was one of four signings at Barca last month, along with Ferran Torres, Adama Traore and Pierre-Emerick Aubameyang, but UEFA regulations only allow clubs to add three more players to their European squads midseason.
Head coach Xavi Hernandez has also had to omit youngsters Abde Ezzalzouli and Ferran Jutgla from his plans in the Europa League. Neither player was registered at the start of the season and they do not count as youth players because they have not been at the club long enough.
Dembele does remain eligible to represent the club in Europe, though, despite reports Barca would rescind his contract after he failed to agree a move away from Camp Nou in January.
The French forward is out of contract in June and, given the failure to reach an agreement to sign an extension, Barca told him he had to find a new club before Jan. 31.
However, the transfer window closed with Dembele still at Barca and Xavi must now decide how to use him between now and the summer. He has been left out of the match day squad for the last two matches.
They will face Italian side Napoli in the playoff round of the competition for a place in the last 16. Barca will be at home in the first leg on Feb. 17, with the return fixture taking place at the Diego Armando Maradona Stadium a week later on Feb. 24.