The Iberian rivals clash in Group G in Portugal this evening, with the 35-year-old backing the pair to spring a surprise in this season's competition.
"Teams like Barcelona, Real Madrid and Bayern Munich are the favourites, regardless of whether they are going through a difficult moment. They are used to the pressure," Maniche told Goal.com.
"However, teams like Atletico and Porto could go far if they have a bit of luck. It's not easy to win the Champions League, but anything is possible."
Maniche represented Portugal 53 times during an illustrious career.