Serbia sit fourth in Group I of Euro 2016 qualifying, having suffered a three-point deduction for unsavoury scenes in October's match against Albania, and need a win to get back on track.
Group favourites Portugal are their hosts on Sunday and Ivanovic is not underestimating the size of the task awaiting his side in Lisbon, where FIFA Ballon d'Or holder Ronaldo will be expected to dictate proceedings.
"You're speaking about one of the best players in the history of football, he's not so easy," the Chelsea defender told Perform.
"To be on the top level you have to prove yourself every day, he's doing that game by game.
"He is the guy who knows how to deal with the pressure, for us it will be a big challenge and I hope and I know we have the quality to try to deal with that."
Ivanovic, who celebrated League Cup success with Chelsea earlier this month, recognises the importance of the match as Serbia seek to bounce back from a 3-1 loss to leaders Denmark last time out.
"[It is] a crucial game for us, this qualification especially, because we expect to have more points in the three games, so the game against Portugal is crucial and massive for us," he added.
"We know Portugal is favourite and are a great team but they've lost a game at home against Albania, so we see our chances and we know if we perform well - if we play to the level we know how to play - we can expect some presents and gifts from the game."
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