Agnieszka Radwanska has insisted that an ageing Venus Williams will still present a "great challenge" in the fourth round of the Australian Open.

The Pole was an impressive form as she cruised past Varvara Lepchenko on Saturday to set up a meeting with Williams, who beat Camila Giorgi in three sets.

The 34-year-old American won the last of her eight Grand Slams in 2008, but world number six Radwanska is adamant that she continues to be a dangerous opponent.

"I think playing her is always great challenge," she told reporters. "I think she is still playing great tennis even she's a bit older. She's still really fit and playing a high level.

"I think it's going to be another good match."

Williams currently edges the head-to-head record between the pair, winning five of their nine matches.