Ibrahimovic has been in stunning form of late and the 32-year-old is in buoyant mood ahead of Friday's first leg in Lisbon.
"I feel good, what matters is what I think of myself. I progress all the time and I'm 32, I've never played better than now," the Sweden skipper said.
"[But] it's Sweden against Portugal - do not focus on two players. What matters is the collective, and to succeed we all need to do well."
The visitors, who host the second leg on November 19, will take confidence from their record against Portugal, having lost only three of their previous 15 meetings, but will be keen to break a run of three draws with the Seleccao.
Ronaldo will be key for Portugal as they look to qualify for their third consecutive World Cup, but they have never beaten Sweden at home in seven attempts.
Erik Hamren's men suffered a 5-3 reverse against Group C winners Germany in their final round-robin clash, while Portugal are on a seven-game unbeaten run in their qualification campaign.
Portugal's only defeat in Group F was against eventual winners Russia, with Fabio Capello's men finishing a point clear to claim the automatic qualification spot.
Midfielder Miguel Veloso is the only new concern for coach Paulo Bento after he finished training with pain in his left knee.
Fabio Coentrao (ankle) and Joao Pereira (thigh) were injury doubts when the squad was announced, while William Carvalho would collect his first cap if used.