Chelsea travel to Camp Nou for the first leg of their semi-final on Tuesday night aiming for a positive result to set them up for the return leg in West London next week.
Barcelona are the bookies' favourites to win the competition, but Pique believes their chances of going to the final in Roma are 50-50.
"I think it will be really, really tight, they are a great team as well with a lot of great names and great players," Pique told Sky Sports News.
"It will be really difficult as they have the second game at Stamford Bridge and this could be a little advantage, but I think it is 50-50 our chances to qualify.
"We have to keep going and keep doing the same things we are doing."
AttackingFormer Manchester United man Pique believes Chelsea have become more attacking since the arrival of Guus Hiddink and he was impressed by their quarter-final win over Liverpool at Anfield.
"Since Guus Hiddink arrived it seems like they like to play more attacking," added Pique.
"They are scoring more goals, it is true they are conceding more goals as well, but they are winning and this is the important thing in football.
"They qualified by playing a great game in Anfield against Liverpool. It is very difficult to win there and they won 3-1."