Scott Brown, James Forrest, Georgios Samaras and Kris Commons were all in Celtic's travelling party which checked in at Glasgow Airport on Monday ahead of the trip to Barcelona for the 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."
Defenders Adam Matthews and Kelvin Wilson suffered knee and calf complaints during the win over St Mirren but have recovered.
Former Celtic defender Mjallby watched Lionel Messi score a hat-trick in Barca's 5-4 win over Deportivo La Coruna on Saturday night and admits it will be difficult to snuff out the Argentina superstar.
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."
He added: "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 Lionel Messi, they have another nine (outfield) guys who can play football."
The Scottish champions have taken four points from their first two group games. A goalless draw against Benfica at Celtic Park was followed by an historic 3-2 away win against Spartak Moscow to leave Celtic behind their hosts at the top of the section.
"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," Mjallby said. "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."
- Clydesdale Bank Premier League
- Johan Mjallby
- James Forrest
- Lionel Messi
- St Mirren
- Kris Commons