Barca will go into the semi overwhelming favourites.
"For most people Barcelona are the best team in the world, but in two matches anything is possible," said Kalou.
"I believe that in a Champions League match you can never underestimate an opponent.
"We saw Inter (Milan) with (Jose) Mourinho cause Barca trouble two years ago. We also played great matches against them three years ago.
"We know Barcelona well, but we must forget about the past."