Świątek announced her decision in a statement shared on Twitter on Wednesday, Polish state news agency PAP reported.
The 21-year-old Pole, the defending champion and the top seed in Miami, was expected to play American Claire Liu in the second round on Thursday after receiving a first-round bye, according to officials.
Świątek explained that the rib injury was the consequence of “a strong infection” she had been battling in the winter.
The Polish player in February won the Qatar Open in Doha, beating American Jessica Pegula 6-3, 6-0 in the final.
A week later, Świątek lost to the Czech Republic’s Barbora Krejčiková 4-6, 2-6 in the final of the Dubai Tennis Championships.
Last week, the Pole reached the semifinals of the prestigious BNP Paribas Open in Indian Wells, losing 2-6, 2-6 to the eventual champion, Elena Rybakina of Kazakhstan, on Saturday.
It was after that match that Świątek first hinted at her physical concerns, according to the Women’s Tennis Association (WTA).
At the time, the rib injury did not seem serious enough to force her to withdraw from the Miami Open, the PAP news agency reported.
'A strong episode of tough cough led to a rib injury'
Świątek said in her statement: "You know that in and after Doha I was struggling with a strong infection. I was allowed to play, but a strong episode of tough cough led to a rib injury.”
She added: “We were trying to handle it and continue to play as long as it was safe for me. We were analyzing the data in the last days and my doctor prepared my diagnosis. Unfortunately, I'm still feeling a lot of discomfort and pain and I can't compete."
The Polish world number one stated: “I need to take a break to recover and I have to pull out of the Miami Open and Billie Jean King Cup.”
She added: "I will keep you updated about where I play next, because it depends on my process of recovering and the recommendation of my medical team. I have the best team behind me. We only need some time to deal with the injury.”
'Health is the most important'
“It's a truly difficult call to not play in Miami and BJKC, but health is the most important," Świątek also said.
She concluded: “I’m grateful this is the first health issue in a long time and I was able to compete in perfect shape for so long, but that’s sports, it happens sometimes, without our control … Time to accept it and get well as soon as possible."
Światek will be replaced in the Miami Open draw by lucky loser Julia Grabher of Austria, the WTA said.
Poland's Linette, Rosolska to compete in Miami
Meanwhile, Poland’s world No. 19 Magda Linette, the number 20 seed, was set to play Russia’s Evgeniya Rodina in the second round on Thursday, after receiving a first-round bye, according to organisers.
Linette, 31, was also expected to feature in the doubles competition, alongside American Bernarda Pera.
Another Pole, Alicja Rosolska, was set to compete in the doubles with Monica Niculescu of Romania, the PAP news agency reported.
(pm/gs)
Source: PAP, wtatennis.com
Click on the audio player above to listen to a report by Radio Poland's Ada Janiszewska.