Tuesday's Group H clash at Celtic Park represents the first game that Barca will be without Messi since he hobbled out of the 2-0 victory at Almeria on Saturday with a hamstring problem - an injury that will sideline him for two to three weeks.
The Argentina international has scored 62 goals in 80 Champions League appearances and netted a hat trick in the 4-0 win over Ajax on matchday one earlier in the month.
Fabregas, though, is confident Barca can cope without the 26-year-old superstar and has backed himself and the likes of Neymar to come to the fore against Scottish champion Celtic, which recorded a memorable 2-1 win over the Spanish giant in the group stages of last season's competition.
"Messi is the best player in the world, he makes a difference, but he won't play (against Celtic). We can't do anything about that," said the former Arsenal midfielder.
"Without Messi, we will all have to take more responsibility. We have to step up, don't feel his absence and play football without him.
"I might have more offensive responsibilities. I will try and help the team as a striker or whatever other position I play.
"Now I feel confident, in good shape and the manager trusts me. I am in a good moment. Maybe I need to be more consistent."
On Neymar - who has scored three goals in nine appearances in all competitions since joining Barca from Santos in May - Fabregas added: "We need him (against Celtic) and I think he's ready.
"Mentally he's very strong, pressure doesn't seem to affect him, he has clear ideas.
"Neymar is a star in the making, he'll be important in football, everything is in his hands. He can be one of the greatest."
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