Sam Burgess says fellow rugby league convert Israel Folau is the man England need to stop if they are to beat Australia and keep their World Cup hopes alive.
Defeat on Saturday could see England become the first tournament hosts to bow out of the World Cup before the knockout phase after their agonising 28-25 loss to Wales.
Burgess hailed Folau as an "outstanding athlete".
Burgess's skills as a rugby union centre continue to polarise opinion but there are no such doubts over the worth in the 15-man game of Folau. In 34 Tests for Australia, the 26-year-old full-back has scored 18 tries - a superb strike-rate.
"I've been watching a bit of footage on him and he's an unbelievable athlete," Burgess said of Folau, who also had a brief spell in Australian Rules football.
"He can move off both feet, he's strong, he's able to break tackles, stand in tackles and make things happen, so he will certainly be a threat.
"He's an all-round athlete and to play in three codes at professional level is quite unbelievable," added Burgess, two of whose four England appearances have come at this World Cup.
"He's looking very comfortable in union and he's enjoying his time. It will be tough to stop him on Saturday, but that's the job we have to do."
Fired up Wallabies
Burgess, 26, who started against Wales and will likely be involved in some capacity when coach Stuart Lancaster names his side on Thursday, became an iconic figure in Australian sport during four seasons of rugby league with South Sydney Rabbitohs.
The time in Australia culminated with Burgess, broken cheekbone and all, producing a man-of-the-match performance as the Rabbitohs, owned by Hollywood actor Russell Crowe, beat the Canterbury Bulldogs in last year's Grand Final.
Burgess then joined leading English Premiership rugby union side Bath in October in a bid to force his way into Lancaster's World Cup squad.
Against many predictions, he succeeded and Burgess said England would face another huge test when they went up against the Rugby Championship-holders at Twickenham.
"Australia are very competitive, that's in their nature, plus they're playing England," Burgess said.
"They will definitely come out of the blocks hard and fast. I know (Australia coach) Michael Cheika and I know him pretty well, he will be getting the guys fired up.
"I expect another great Test and challenge and it's something to look forward to. There will not be many bigger occasions than this weekend.
"From us Australia can expect heart. If there's a time to put your body and heart on the line it's this weekend. A winning attitude is what we need on Saturday for 80 minutes."
Meanwhile Burgess became the latest England player to dismiss comments made after the Wales defeat by former captain Will Carling that Lancaster had created a "classroom" environment where players were treated like "schoolboys".
"I've not seen Will around training, he's not been around while I have been in so I'm not sure how much inside knowledge he has," said Burgess, whose inclusion in England's World Cup squad was also criticised by former centre Carling.
"It's our environment. We don't need to explain what it is because one person has made a comment. We're comfortable with what we're doing."