Portugal go into the match leading 1-0 from the first leg - Ronaldo scored the only goal with a diving header - but Larsson believes the appointment of an English referee could be crucial to Sweden's hopes of making the finals in Brazil next summer.
Ronaldo won a number of free-kicks during the first leg but Sunderland midfielder Larsson told media in Sweden: "We have an English referee now so we can probably go in a bit harder.
"I do not think he is going to fall for the same tricks so easily.
"Howard Webb is used to refereeing where the game is a little more physical. He's a great referee, too, which is important for such a big game."
Sweden have been preoccupied with how little of the ball Zlatan Ibrahimovic saw during the first leg, and there have been calls for 37-year-old midfielder Anders Svensson - once of Southampton - to start the second leg in order to provide better service for the Paris St Germain forward.
Larsson think that Sweden should keep it tight but play higher up the pitch.
He said: "We cannot go out all guns blazing but we must have a more attacking game with more ball higher up the pitch, then we will get Zlatan more in the game."
Ronaldo has himself previously expressed a liking for playing in matches under Webb, who will have the same assistants in Mike Mullarkey and Darren Cann as officiated with him at the 2010 World Cup final. Another Premier League referee, Andre Marriner, will act as fourth official.
"The truth is I like this referee a lot," said the Real Madrid star earlier this year. "He is English, he has refereed many of my games there and I like him a lot."
There is nervousness about the match in Portugal with media pointing to the fact that the temperature will be around freezing point, and that the pitch is not in a very good condition.
Former Manchester United winger Ronaldo is expecting "another battle".
He said: "Portugal have a small advantage, and we are expecting a very difficult game, but we are ready.
"We will have to be fully focused. More than anything else, these players want to be in Brazil, so we will give our best to get there."