Defending champion Iga Swiatek pulled out of the Miami Open on Wednesday because of a rib injury. (More Tennis News)
The No. 1-ranked Swiatek was supposed to face Claire Liu in the second round on Thursday.
As a seeded player, three-time Grand Slam champion Swiatek received a first-round bye in the hard-court tournament that she won a year ago during a 37-match unbeaten run that was the longest in women's tennis in a quarter of a century.
Swiatek, a 21-year-old from Poland, said after a 6-2 6-2 loss to eventual champion Elena Rybakina in the BNP Paribas Open semifinals on Friday that her rib was bothering her.
"I still have to run some tests and see what's going on. I don't know yet," Swiatek said on Friday.
Instead of playing Swiatek, Liu will go up against 94th-ranked Julia Grabher, who lost in qualifying, but now gets to move into the draw.
Liu advanced on Tuesday when her first-round opponent, Katerina Siniakova, stopped playing in the second set because of a hurt wrist.