Barca have 10 confirmed positive cases among their first-team squad and a further seven players either suspended, injured or a doubt for the game at San Moix.
However, LaLiga rules state that fixtures should be played if clubs have at least five first-team players available and can field a 13-man squad, with at least one goalkeeper, by drawing on the reserve team.
“We will turn to the B team and we will go there to win the game, but we have 17 players missing,” Xavi said at a news conference.
“I am worried. It seems crazy to me that [LaLiga] won’t suspend it. It makes no sense to play. We’re at the very limit. Common sense should have prevailed.
“The rules are very tough. Mallorca are in a similar situation, albeit not as severe. It’s chaotic, but we will go there for the three points.”
Xavi says Umtiti has since tested negative and could yet feature against Mallorca, but Sergio Busquets will definitely miss the game through suspension.
Despite that, Xavi still has at least nine first-team players available — Marc-Andre ter Stegen, Neto, Ronald Araujo, Eric Garcia, Gerard Pique, Oscar Mingueza, Frenkie de Jong, Riqui Puig and Luuk de Jong — which means the game must go ahead.
B team players Nico Gonzalez, Ferran Jutgla Alvaro Sanz, Arnau Comas, Mika Marmol, Guillem Jaume, Lucas de Vega, Ilias Akhomach and Estanis Pedrola have all been training with the first team to make up the numbers this week.
Meanwhile, Xavi added that he’s not given up hope of tying Dembele down to a new deal despite a setback in negotiations this week.
Dembele, 24, is out of contract in June and is now free to talk to other clubs with Barca and his agents still unable to reach an agreement over new terms.
“I am not disappointed,” Xavi said of the situation. “It’s a negotiation. Sometimes advisors and agents can be difficult. But Barca’s position is clear and the process is ongoing.
“I am optimistic and I hope that Ousmane will make an effort [to renew]. He has a fantastic offer. There’s always a back and forth.”
Xavi also confirmed that tying Dembele down to a new deal would allow Barca the financial room to register “one or two signings” in January.
By getting the forward to commit to the club, Barca can spread the remaining amortisation payments on the transfer fee they paid for him in 2017 over the length of his new terms, creating room within their LaLiga-imposed spending limit of €97 million for the season.