Rafa Benitez has revealed Yerry Mina will miss Sunday’s Premier League fixture at Crystal Palace (4.30pm GMT) after sustaining an injury in Monday’s 2-1 victory over Arsenal.
Benitez added Allan took part in “half of the training session” on Friday and the midfielder's fitness will continue to be assessed ahead of the game at Selhurst Park.
Salomon Rondon has recovered from the knock that kept him out of the Arsenal clash and is in contention for selection.
Dominic Calvert-Lewin will not be available for Sunday’s game, but Benitez explained he is “getting closer” to making a return from a quadriceps injury.
Tom Davies, meanwhile, remains sidelined with a knee problem but could return to training next week.
Speaking at his pre-match press conference on Friday afternoon, Benitez revealed his satisfaction with the collective fitness levels in the squad – and explained how the Blues' physical output in Monday's dramatic Goodison Park victory set a new standard for his team.
"Against Arsenal, I think it was the game where we ran more [than in any other match] in four years," he said.
"That means a lot. It means the team is physically at a good level. You can always improve but at the moment we are fine and working so hard.
"In terms of injuries, we still have Yerry unavailable. Dominic is getting closer with every training session he is doing with the rehabilitation coach.
"He is getting better.
"Rondon is available and has been training and Allan today [Friday] has done half of a training session.
"Then we have Tom Davies, and maybe next week he will start [training] with the team."
Benitez also outlined how the Club is taking every possible step to reduce to possibility of COVID-19 transmission.
The Government announced this week that new Plan B restrictions will be introduced in England following the emergence of the Omicron variant.
Tottenham Hotspur, meanwhile, were forced to postpone their Europa League meeting with Rennes on Thursday and Sunday's Premier League game at Brighton & Hove Albion after a number of positive cases among players and staff.
"It is a difficult time with COVID-19 around," Benitez added. "We are having meetings with the players and following the emergency measures, which we have to do.
"We have seen some clubs affected and we have to be sure we are doing what we have to do. This busy time, around Christmas, is always complicated because there are so many games.
"The only thing we can do is to make sure we keep our distance, wash our hands, wear the masks and tell the players what we have to do.
"It is difficult for everyone. I think it complicated, but we have to manage and be sure we take the measures we have to do."