The Catalan side currently top the Liga table with an 11-point advantage over second-placed Atletico Madrid, while Jose Mourinho's men sit in third spot, already 15 points behind the leaders.
However, the 45-year-old does not believe the current standings of the two clubs should give his players a reason to become complacent.
"We still don't feel we are the favourites," he told reporters.
"This is a knockout fixture and there are two legs. There is no clear favourite."
Lionel Messi put on another outstanding performance, scoring four goals during Barcelona's 5-1 win against Osasuna on Sunday and Roura spoke about his delight at working with the Argentine on a daily basis.
"When you live and work alongside him, you take it all very calmly, but when you stop and think, you raise your hands in astonishment".
He also talked about regular contact with coach Vilanova, who is still undergoing treatment following a cancer relaps in December, ensuring that the trainer still plays a major role when it comes to decision-making.
"We are in constant contact, and he sees the games. We talk about all the decisions to be made," he noted.
Barcelona's clash with Real Madrid kicks off at 21.00CET on Wednesday, January 30 at the Santiago Bernabeu.