(MENAFN - Kora) The Euro 2004 runners-up were the first side drawn in Group I before being joined by Denmark, Serbia, Armenia and Albania in the only five-nation pool.
Hosts France, who are already assured of a place in the finals, will play friendlies against each team in Group I.
First and second from all nine groups are guaranteed to join France in 2016, while the best third-placed side will also go straight through.
The remaining eight teams to finish third will battle it out in the play-offs and, although Bento believes Serbia and Denmark will prove worthy adversaries, the former Sporting Lisbon defender thinks he holds an ace in the pack in the form of Real Madrid star Ronaldo, winner of the 2013 Ballon d'Or.
Ronaldo's brilliance saw him score all four goals as Portugal defeated Sweden 4-2 on aggregate in November in the play-offs to reach this year's FIFA World Cup.
Bento said: "It is a difficult group, I have to say. The level of the top national teams is similar.
"It is very equal and it will be tough, but we have one point in our favour; we have the best player in the world (Ronaldo).
"Cristiano works well at everything. He is a fantastic professional and now he is an ambitious player.
"He always wants to be a better player. It is incredible, but he is still improving as a player and everybody expects a lot from the best player in the world."
Portugal have failed to convince in each of their last two European Championship qualification campaigns, finishing second to Poland before Euro 2008 and Denmark for Euro 2012, and Bento insists the current crop have to put that right this time around.
He added: "The last two qualifications were not so good, but this time it is different because the first two teams qualify directly and the best third placed.
"It is important to have a better qualification than the last Euros. It is difficult to say (who will pose the biggest threat), but Denmark, Serbia and Portugal are the strongest teams (in the group).
"Between these three will be the qualifiers. It will be equal, not easy. It is a tough group."
Denmark coach Morten Olsen added: "We have finished ahead of Portugal in previous qualification tournaments, while Serbia are a quite unknown factor.
"However, from what I have heard from the Belgians, who met them in the latest qualification tournament, they are a team in progress, and Belgrade is always a difficult place to play."