(CNN) -- Her popstar boyfriend has written a song about her "heart of a champion," but Victoria Azarenka is struggling to get on court at the moment.
The Belorussian is unbeaten in 17 matches this year, but she has now suffered her third withdrawal of the season after a late pullout at the Miami Masters on Friday.
She cited the ankle injury that forced her to miss last week's quarterfinal against Caroline Wozniacki at Indian Wells, allowing Maria Sharapova to take the No. 2 ranking spot from her.
"The last two days I tried to practice, which did not get better so it just gives me a very obvious indication that it's not possible for me to play," Azarenka told reporters at Key Biscayne, where she was champion in 2009 and 2011 and this year had a first-round bye.
"Today I went on the court and I got more pain. I cannot really move. It makes me very frustrated."
The Australian Open champion has been dating LMFAO's Redfoo, whose new song "Heart of a Champion" samples the tennis star's trademark grunting and includes the lines "You gotta start aggressive, Keep your feet moving, You gotta really want it, With everything you're doing."
It even apparently alludes to her controversial Australian Open semifinal against Sloane Stephens, when the 23-year-old angered fans by taking a lengthy medical break at a crucial point in the match against the U.S. newcomer, citing breathing difficulties.
The chorus includes: "When you're losing your breathing, Your body is sore, To be the last one standing, In the eye of a storm, It takes the heart of a champion."
Redfoo, the son of Motown Records founder Berry Gordy, is a keen tennis player himself and has entered in regional qualifying playoffs for this year's U.S. Open.
The 37-year-old rapper will try to get through in both singles and doubles, in which he will partner Ayaka Okuno, 17, who he has been coaching.
"It's always been a dream of mine to play professional tennis," he said in a statement last week.
Azarenka's withdrawal allowed 19-year-old Lauren Davis into the main draw, and she took her chance -- saving three match points against Madison Keys before beating her fellow American 6-1 5-7 7-6 (9-7) in the second-round match.
There was also a walkover in the men's event in Miami, as third seed David Ferrer progressed to the third round after Russia's Dmitry Turnsunov pulled out due to illness.
The Spaniard will next play Italian 32nd seed Fabio Fognini.