The 22-time major winner Nadal, who is making his competitive return at the Brisbane International after missing nearly a year due to injuries, has not played against Murray since 2016.
Defending champion Iga Swiatek along with Australian Open champion Aryna Sabalenka top the entry list for the Miami Open 2023, which begins March 21 at the Hard Rock Stadium.
The 25-year-old revealed the news in a social media post, penning a heartfelt note to fans in both English and Japanese that accompanied a photo of an ultrasound.
Veteran Venus Williams also withdrew her name from the first Grand Slam of the year after suffering an injury at the ASB Classic in Auckland, New Zealand.
Zhang Shuai produced a stunning performance to advance to the second round of the tournament, defeating Osaka 6-4, 7-5 in a match that lasted for 75 minutes.