Busquets is facing a spell on the sidelines with the ankle injury that he picked up in the team's 3-0 victory over Sevilla in La Liga last weekend.
Dembele, meanwhile, suffered a hamstring problem at the end of January, and the France international is not expected to be back on the field until the middle of next month.
A timeframe for Busquets has not been set, although it is believed that the experienced midfielder will be missing for the remainder of the month.
Barcelona otherwise have a full squad available for this match, while there is another spot in the selection for teenage forward Angel Alarcon.
During his pre-match press conference, the Catalan club's head coach Xavi picked out Yellow Submarine duo Dani Parejo and Pepe Reina when discussing Villarreal's threat this weekend.
"Villarreal are a great team with a philosophy very similar to ours. Parejo is an extraordinary player and Pepe Reina is very good with his feet," he told reporters.
Xavi also insisted that he is not prioritising La Liga over the Europa League, as Barcelona prepare to welcome Manchester United for the first leg of their knockout round playoff next Thursday.
"I don't prioritise La Liga over the Europa League. We want to win every game and we give the same importance to all competitions," the head coach added.
Xavi, meanwhile, refused to give any indication of his formation on Sunday evening, with the Spaniard needing to bring in a replacement for the injured Busquets.
"I never explain the team's ideas in advance but we will decide tomorrow. Busquets's loss is important, we will miss him especially when it's time to pause," said the Spaniard.
Barcelona will be bidding to make it 11 straight wins in all competitions on Sunday night.
Barcelona squad vs. Villarreal:
Ter Stegen, Pena, Tenas; Araujo, Christensen, Alonso, Alba, Roberto, Kounde, E Garcia, Balde; Gavi, Pedri, Kessie, F de Jong, Torre; Lewandowski, Fati, F Torres, Raphinha, Alarcon