The Portuguese giants are set to play host to the Magpies on Thursday in the first leg of their quarter-final clash.
John is aware that Benfica are being billed as strong favourites to progress, but he insists they are taking nothing for granted.
The Holland international feels Newcastle will offer a considerable threat and believes a positive performance on home soil is crucial.
John told Sky Sports: "Newcastle are a good team. This round is not easy because games against English teams are always complicated.
"The key to this round is to obtain a good score in Lisbon, allowing us to manage the second match better.
"For me, the main man to stop will be Papiss Cisse. He is a dangerous forward who is capable of getting goals and if we can stop him then we increase our chances of going through.
"People may be thinking that Benfica are favourites, but I think it is 50-50.
"I am happy with how my first season in Portugal has gone, but I want to win titles. This Europa League is our dream and we believe we can make the final, but for now we are focused on Newcastle."