<text>  Portugal may have one of the best players in the history of football in the form of Cristiano Ronaldo but Branislav Ivanovic is confident his Serbia side can nullify the threat of the Real Madrid star on Sunday night. Serbia currently occupy fourth place in the Group I standings ahead of their clash with Portugal who sit just one point behind pool leaders Denmark. Youre speaking about one of the best players in the history of football, hes not so easy, Ivanovic told Perform. Cristiano Ronaldo left vies for possession with Jose Fontes during Portugal training on Thursday . Ronaldo, Ricardo Quaresma left and Vieirinha are gearing up for the visit of Serbia on Sunday night . To be on the top level you have to prove yourself every day, hes 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. Ivanovics side were deducted three points following their 3-0 win against Albania in October when an unmanned drone carrying a pro-Albania flag flew over the Partizan Stadium in Belgrade and resulted in a melee between the two sets of players and some Serbian fans. A 3-1 loss to Denmark in November has heaped further pressure on Serbia and Ivanovic concedes that Sundays game is a must-win game for his side. Branislav Ivanovic left is hoping a win over Portugal can re-ignite Serbias bid to reach Euro 2016 . 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, the Chelsea defender added. We know Portugal is favourite and are a great team but theyve 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. Serbia were deducted three points following their 3-0 win against Albania in October when an unmanned drone carrying a pro-Albania flag flew over the Partizan Stadium in Belgrade resulting in ugly scenes . 