Victoria Azarenka expects British number one Johanna Konta to provide a severe test when they meet at the Miami Open on Wednesday.
Azarenka is the WTA Tour's form player after her Indian Wells win, but Konta is rising fast through the rankings.
They meet for the second time, after the Belarusian retired at a set down in Wuhan last September.
"It was difficult to consider that a full match since I didn't feel physically well," said Azarenka.
"But it's really impressive to see how much she improved over the last couple months."
Their quarter-final is scheduled for the evening session in Miami.
Azarenka, ranked eighth, beat world number one Serena Williams to win in Indian Wells earlier this month, and looks to be back to the form that won her two Australian Open titles, before two injury-hit years.
However, Konta is on the verge of a place in the top 20 having been ranked 151st in the world this time last year.
"She obviously had some great results, playing with a lot of confidence," added Azarenka. "She has a very solid game, big serve.
"I'm just looking forward to that challenge. I think for me it's going to be our first meeting, but I'm looking forward to that."
Konta, 24, is the first British woman to reach the last eight in Key Biscayne and would break the top 20 if she reaches the final.
"It will be an incredibly tough battle," said the world number 23.
"Azarenka has had an incredible season so far. I'm going to have to really run down every ball, fight every single point and we'll see what the day will hold."