Fernando Santos' side have had a mixed start to their campaign with two wins coming after their surprise opening defeat to Albania, leaving them second in the group behind Denmark.
However, with Morten Olsen's side not in competitive action during this international break, Portugal could go top with victory this weekend.
"We are aware that if we win it will be an important step, but after this game we still have more games," said the Sporting Lisbon midfielder.
"We must continue to work to guarantee victory.
"We have seen the videos of Serbia's games and the movements of the players, so we have an idea [of how they will play]. We know they have excellent players, but if we impose our game I am sure that the victory will be assured."
Santos received a boost ahead of the clash with the return to training of Real Madrid defender Pepe, while his illustrious club-mate and international captain Cristiano Ronaldo will once again be key to their progress.
Serbia's campaign has been fraught with controversy and they will be desperate to get back to things on the pitch to keep them competitive in the group.
Radovan Curcic's side have just one point from their opening three games, having been deducted three points awarded following their match with Albania in October, which was infamously abandoned after a drone carrying an inflammatory flag flew over the pitch and sparked fights between players.
Southampton forward Dusan Tadic played in that game and he admits it set them back as they look to qualify for the European Championships for the first time as a sole nation.
"This really damaged us, but in our country when something is difficult we get better and better," he told Perform. "We have something inside to show that we are all together and we can handle it.
"It was really disappointing for us because we were really comfortable and had a lot of confidence that we were going to win that match, in the end they took points and you don't feel like a winner."
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