The likes of Varndell and Tait, both 20, are sure to face a tough task against Stirling Mortlock, Lote Tuqiri and Chris Latham.
However, 34-year-old Catt predicted that both men would prove their worth against the world-class Wallabies attack.
"The good thing from my perspective is they have been consistently good all season and that's a sign that they are very confident in their ability and very confident in what they're capable of doing," said Catt.
"Mathew Tait has had a lot of press about him and he's capable of standing up. Against the Barbarians I thought he played very, very well.
"It is a massive challenge for all of us, especially young backs to come to Australia and take on the likes of Mortlock and Tuqiri.
"But these youngsters these days have got a hell of a lot of confidence and they know exactly what they can achieve.
"They're very, very quick on their feet, a bit like Matty Giteau, they evade the tackles and then they've got the gas to burn."
Fullback Tom Voyce agreed it would be a good contest for the English backline, even though Australia named nine rookies in their 33-man squad last week.
Australia have also been forced to accept that Giteau - on his way back from knee surgery - will miss the first Test on July 11 in Sydney.
But Voyce warned: "They're going to be very dangerous.
"I think they're bringing in some new young talent as well so I think it's going to be an exciting time for them as well.
"They're certainly going to be a big threat to us so we've got to be on our mettle.
"Missing Giteau is going to be a big thing for them, but I think they've got dangerous men all over the board really."
The main player Voyce singled out for particular attention was blockbusting winger Tuqiri.
"Lote is a quality player, world class, and coming up against someone like him, you've got to be really aware of what he's up to so to have that challenge will be great," said Voyce.
"I think all the boys are going to have to be aware of him, of his ball carrying, and he's a very strong runner."