Liverpool beat their North West rivals 2-1 at Anfield in September and followed that in March with an historic 4-1 demolition at Old Trafford.
But Reina said: “The truth is that it is not easy to beat Manchester United twice in a season.
“The key was that we approached both games with nerve and played a passing game from man to man. That is the way to do most damage.
“I believe Barca will play that way and I hope they win because they are a Spanish team and because I don’t want our rivals winning titles.”
Meanwhile, reports in Holland have suggested Liverpool are tracking Feyenoord’s highly-rated 16-year-old striker Luc Castaignos, the top scorer at the recent European Under-17 Championships.
