The two sides meet for the first leg of their last 16 tie at the Santiago Bernabeu in Europe's elite competition on Wednesday.
Despite his confidence, the Argentine forward is well aware that United will be a tough match for the La Liga champions.
He told the Bwin website: "[United] are quite a compact team. They always make it to the knockout rounds in European competition and we're going to have to be on our toes.
"But we can do a lot of damage with individual quality and with counter-attacks, although we can't forget we need to have a solid defence, a winning mentality and team spirit."
The two sides meet at the Santiago Bernabeu on Wednesday.