The Scottish champions shocked their Spanish counterparts in the group stage last season as they reached the last 16 of the competition.
However, Commons wants the Hoops to forget that triumph and treat the upcoming fixture in Group H like any other match.
"From an outsider looking in you can see that they're superstars but when you put your shirt and boots on, and get out there, it's just another game," he told the club's official website.
"If you start getting too carried away about who you're playing against, and what the occasion is, then you will lose your concentration, so you have to approach it like any other game."
Celtic were beaten 2-0 by AC Milan in their opening match of this season's Champions League.