Everton face an anxious wait to learn the full extent of Allan's hamstring injury with Carlo Ancelotti not yet able to put a time-scale on his return.
The Brazilian was stretchered off just before half-time in the game with Leicester City after injuring his right leg.
Allan pulled up as he chased back when Leicester hit the Blues on the counter-attack and had to be replaced by Andre Gomes.
The 29-year-old had picked up where he left off against Chelsea and was influential in helping Everton keeping their 1-0 lead intact at the King Power.
Allan now faces an extended spell on the sidelines but Ancelotti was unable to say how long he was going to be out for.
Everton face Arsenal at Goodison on Saturday before the Carabao Cup quarter-final with Manchester United on Wednesday and the Boxing Day trip to Sheffield United.
Manchester City are the visitors to Goodison before December is out.
“We have to check on him in a few days and then we will see how long [he will be out],” Ancelotti said.
Ancelotti, meanwhile, described the wrist injury sustained by Richarlison, which required the forward to wear strapping in the second-half, was “no problem” and that it was merely a “twist”.
The 2-0 win over Leicester has taken the Blues to fifth in the table after 13 games of the season played.
“We are where we want to be,” Ancelotti said.
“If the season finished today then we would be satisfied. Unfortunately, the season is so long so we have to keep fighting to stay in this position.”
