"Physically they're very strong, they've improved a lot and they've been wanting to go to the World Cup for a long time. That's a big factor," said Brazilian-based centre half Lugano on Thursday.
"It's going to be more difficult than Argentina."
Uruguay beat second-placed Argentina 1-0 in Wednesday's qualifier to clinch fifth position in the South American group and earn the two-legged playoff against Australia for a berth in next year's finals in Germany.
Australia and Uruguay also met in a playoff in 2001 when the South Americans won 3-1 on aggregate.
Previously, Australia fell at the last hurdle to Scotland, Argentina and Iran.
Uruguay host the first leg on November 12 with the return in Sydney four days later.
Eugenino Figueredo, the Uruguayan Football Association president, said on Thursday that he wanted to bring forward the Montevideo leg by one day to allow more time between the two games.