MELBOURNE (AFP) - Rafael Nadal faces his toughest test yet at the Australian Open on Wednesday (Jan 25) with a quarter-final clash against big-serving Milos Raonic, while Serena Williams also has a stern challenge ahead.

The Spanish 14-time Grand Slam champion is bidding to end a major title drought stretching back to the 2014 French Open, and Canada's Raonic could easily make like difficult.

"It's going to be a very tough match and I need to be very focused with my serve and play aggressive," Nadal said ahead of the feature evening match on Rod Laver Arena.

"If I am not playing aggressive, then I am dead."

One element that could work in his favour is that Raonic suffering from the after-effects of 'flu, although the illness has not stopped him racking up dozens of unplayable aces as he has powered through the draw.

Third seed Raonic, the highest-ranked player still standing in the men's draw, said he hoped to be back to 100 percent by the time he faces Nadal.

"I believe so, with the way things are going, I'm getting better and better," he said.

Whoever wins will face either Bulgaria's Grigor Dimitrov or Belgian David Goffin, who take to the court in the afternoon session.

Dimitrov, who will be playing in his third Grand Slam quarter-final, downed Goffin in their only meeting in the third round at the 2014 US Open.

In the women's draw, Williams will have a confident Johanna Konta on the other side of the net as she tries to join sister Venus in the last four.

Gunning for a record 23rd Grand Slam title to surpass Steffi Graf and a return of the number one world number ranking, it won't be easy for the second seed.

Konta, the British ninth seed is on a nine-match unbeaten run and she has looked extremely solid ahead of her first career meeting with Williams.

"She has a very attacking game. I know her game pretty well. I look forward to it," said Williams, who is targeting a seventh Australian title.

The winner will play either unseeded Croatian Mirjana Lucic-Baroni or fifth seed Czech Karolina Pliskova, who open the day's proceedings on centre court.

Lucic-Baroni, 34, has become a crowd favourite after her unexpected run to a first Grand Slam quarter-final in 18 years.

She made the Wimbledon semi-finals in 1999 aged 17 before her career fell apart, but has been riding popular support and Pliskova is not underestimating the threat she poses.

"She has to be playing well when she's in the quarter-finals," said the Czech, who made the US Open final last year and is tipped as a future champion.

"I have to be really ready on my legs, serving well. I think I have good chance."