Ibrahimovic, who has scored in the three European matches he has played for Milan this season, will take on Barca for the first time since leaving the club in the summer of 2010 after just one year with the Catalan outfit.
The Sweden striker openly criticised Barca and Guardiola in his autobiography this month, but Guardiola has vowed to "act like sportsmen" if the two meet.
"If we meet I'll be spontaneous and I'll greet him," Guardiola told a pre-match press conference.
"He's a formidable player and he helped us a lot during his time at Barcelona.
"I don't have any problems with Mr Ibrahimovic. I've said it before, being real and natural is the most important thing.
"If we meet, we'll act like the sportsmen that we are."