Both sides were relegated last season, with Reading dropping down from the Premier League and Posh falling to League One.
Peterborough have flown out of the traps in the third tier, winning all four of their league matches so far to sit joint top with Leyton Orient.
"It's going to be a very hard game - going to Peterborough is never easy," Karacan told Reading's website ahead of the trip to London Road.
"They've started this season flying, they've got some great players and I think they'll do well in League One this season.
"I've played Peterborough many times and it's never been an easy game. They've been our bogey team away from home over the years - they've got some great players in [Lee] Tomlin and [Tyrone] Barnett."
Reading have picked up five points from their first four matches back in the Championship and lie 13th in the table.