The driver died aged 41 on Thursday after "overwhelming complications" from the illnesses.
Nascar champion Kyle Busch died of pneumonia and sepsis, family says 2 hours ago Kayla Epstein Getty Images Nascar champion Kyle Busch died after severe pneumonia progressed into sepsis, his family has said in a statement released to The Athletic.
A medical evaluation showed the illness resulted "in rapid and overwhelming associated complications," the statement said.
Busch died suddenly aged 41 on Thursday after what his family had described as a "severe illness".
In a statement, Nascar described Busch as a "rare talent, one who comes along once in a generation". He had won two Cup Series titles and 63 races.
Busch was in the middle of his 22nd season in Nascar's top division at the time of his death.
He had been expected to compete in an upcoming race this weekend, the Coca-Cola 600, at the Charlotte Motor Speedway in North Carolina.
He is survived by his parents, his wife, and two young children.
At a press conference, Nascar CEO Steve O'Donnell said the races would continue, as Busch would be upset if they did not go ahead.
"So we're going to honour his memory," O'Donnell said.
Busch's number and his truck were on display ahead of the event, according to local media.
"Kyle Busch lived just about every chapter of what you could do in Nascar," said O'Donnell, who described the late driver as fierce, competitive and "always good for a great quote".
O'Connell also praised Busch's charity work, citing the foundation he started with his wife to support awareness and advancement for IVF and infertility treatments.
In addition to his winning record, Busch also built a larger than life persona in the racing world and was known by the nickname "Rowdy".
Other tributes poured in following the announcement of Busch's sudden death.
"Absolutely cannot comprehend this news," former teammate Denny Hamlin wrote on social media. "We just need to think of his family during this time. We love you KB." Over the course of his 20-year career, Busch won 234 races in NASCAR's top three series, more than any driver in history, according to ESPN.
Nascar champion Kyle Busch dies aged 41 United States
