Scott Brown, James Forrest, Georgios Samaras and Kris Commons were all in Celtic's travelling party which checked in at Glasgow Airport on Monday morning (Scottish time) ahead of the trip to Barcelona for Tuesday night's (Wednesday morning AEDT) Champions League clash with the Group G leaders at the Nou Camp.
All four missed Saturday's 5-0 Clydesdale Bank Premier League win over St Mirren in Paisley with various ailments.
Assistant Johan Mjallby said: "They are in the squad which means they are in contention.
Former Celtic defender Mjallby watched
He said: "I was there watching it live and what can you say, he is up there with the best to grace the game.
"He is just fantastic.
"I don't know how you can stop him. He doesn't really play as a recognised striker.
"What they do, if you are a centre-half, is take you out of your comfort zone and that is something you don't like.
"So we need to tell our defenders that they are going to be out of their comfort zone and need to gamble a wee bit, and that they can't count on their team-mates to give you cover.
"Sometime you are going to end up one versus one with a Barcelona striker and you have to live with it.
"We know we can't switch off for a second, we know they are brilliant going forward.
"But we are not going to focus on
The Scottish champion has taken four points from its first two group games.
A goalless draw against Benfica at
However, Mjallby is well aware of the task that awaits Celtic.
He said: "We want to get something out of it but we are not daft. We are going to play one of the best teams in the world and they are awesome going forward.
"They are going to be massive favourites.
"We will think of a way to stop them but we can't just sit in and defend, it's not the type of football we play.
"When we get the ball we need to make sure we don't panic and we keep it, but obviously it is going to be a difficult task.
"They are a brilliant team but that's what this competition is about, it is a great challenge for us.
"Instead of being afraid and showing them too much respect we should see this is as a big challenge for us.
"This group of players are improving all the time and hopefully we can catch them on a bad day and upset them."
UEFA Champions League
Turkish side Fenerbahce could face another ban from the UEFA Champions League after UEFA announced the club and five officials will have match-fixing charges heard by its disciplinary body later this month.