"I evolve all the time and even if I'm 32 now, I have the feeling that I keep improving and that I've never played this well," the Swedish captain said during a press conference at Stockholm's stadium Friends Arena.
"For that, one has to train hard, be mentally strong and have the experience I have after playing with fantastic players and clubs," he added. "I hope this can continue."
The two teams meet in Lisbon on Friday with the return in Stockholm next Tuesday.
Ibrahimovic is at the peak of his game both with the national team, for whom he has scored 11 goals in a year, and with Paris Saint-Germain, for whom he scored a hat trick in last Saturday's 3-1 victory over Nice.
Asked about his chances of winning his first Ballon d'Or, he said he faced tough competition from the likes of Franck Ribery, Lionel Messi and Cristiano Ronaldo.
"For me, Ribery has been great so far. He won all the competitions this year and played a central role in doing so. Then there's Messi, who I see as pure talent. He's a natural-born football player, not the result of training. And Ronaldo does it fantastically well. All of them have a very high level," he said.
He highlighted that a supreme all-round team effort would be required to beat Ronaldo's Portugal.