But after the surprising quality and resolve of Hungary and Iceland, the loser of this game could struggle to reach the knock-out rounds.Portugal were dominant in the first half against Iceland, but their wastefulness in the final third cost them as Birkir Bjarnason earned the minnows a point, while Austria, a dark horse for many before the tournament began, were overcome by Hungary.Now, defeat is not an option for either, especially Austria, whose place in this championship would be hanging by a very thin thread.Portugal need the iconic Cristiano Ronaldo on fire, while Austria will demand more from the likes of David Alaba and Marko Arnautovic.This should be an open game, as both teams desperately try to record their first win.TeamsPortugal may make changes after their disappointing draw with Iceland, with 18-year-old midfielder Renato Sanches and Sporting Lisbon's William Carvalho pushing hard to start.Ronaldo and Nani are expected to continue their partnership up front, while tricky midfielder Andre Gomes is also assured to start after an impressive opening game.Austria are without centre-back Aleksandar Dragovic after his red card against Hungary, with Watford's Sebastian Prodl expected to come in.Coach Marcel Koller is likely to stick with his disappointing forwards against Portugal, which would mean Arnautovic and Marc Janko retain their places.Ones to WatchPortugal: Cristiano RonaldoIt sounds obvious that a two-time Ballon D'Or winner would be the one to watch, but the focus on Ronaldo is more because of his poor recent form.The striker was clearly unfit in Real Madrid's Champions League final win, and he was off the boil again against Iceland.If Portugal stand any chance of winning this competition then they need their talisman to be at his best, and so far he has failed to deliver.After the 1-1 draw, Ronaldo slammed Iceland's style of play and he has been criticised for his attitude by current and past players."He thought he could have goals handed to him on a plate," said former Iceland Hermann Hreidarsson."If he would have worked as hard as every Icelandic player, he wouldn't have had to say anything because I'm sure he would have got his rewards."He didn't fancy it on the day and he just got beaten up."Austria: Marko ArnautovicAustria need goals on Saturday and with Portugal possessing a pair of ageing centre-backs in Pepe and Ricardo Carvalho, forward Marko Arnautovic will be key.The Stoke City player has had a chequered career to date, but he found consistency in the Premier League last season and has nailed down the spot on the left of Austria's attacking three. Coach Marcel Koller is desperate his form improves after a poor display against Hungary, and hopes his settled home life can be the catalyst."It's always been important to look at his qualities as a footballer, he's always had ability from that perspective but he wasn't necessarily able to harness that ability on the pitch," he said."It is important that he has confidence even if he makes a mistake. Right from the outset, we knew we needed to support him, to try and talk to him, to try and help him to improve."I think he really has adapted very well. He has his own family, he has got a wife and two kids, he has calmed down and we are delighted he is finally able to harness his ability as a footballer on the field, and he can really help us."Head to head recordThis will be the first meeting between the sides at a major tournament, and Austria hope to register their first win over Portugal since 1979.However, they boast the better overall record having won three of their 10 matches and losing just twice, although this will be their first meeting since they drew 1-1 in a European Championship qualifier in 1995.Did you know?Bayern Munich-bound midfielder Renato Sanches became Portugal's youngest ever player at a major tournament when he came off the bench against Iceland.The highly-rated 18-year-old beat the record of Ronaldo, who was 19 at Euro 2004.