Getty

Signage is seen honoring the late Kyle Busch ahead of practice for the NASCAR Craftsman Truck Series North Carolina Education Lottery 200 at Charlotte Motor Speedway on May 22, 2026 in Concord, North Carolina.

A sports medicine physician took to social media Friday morning to raise a disturbing medical theory about what may have caused the death of NASCAR two-time Cup Series champion Kyle Busch, who died Thursday after reportedly collapsing inside a Chevrolet racing simulator facility in Concord, North Carolina.

The symptoms described in 911 call audio acquired by TMZ Sports include overheating, difficulty breathing, and blood in his cough. That description prompted a Florida-based sports medicine doctor, Dr. Jesse Morse, to immediately think about a possible blood clot.

Doctor Raises Blood Clot Theory in Kyle Busch Death

No official cause of Busch’s death has been released. But posting on his X (formerly Twitter) account Friday morning, Dr. Morse wrote that Busch’s reported coughing up blood had him “concerned for a blood clot,” citing multiple possible contributing factors, such as an active infection, a leg injury Busch had sustained roughly two months earlier, and other variables.

Morse laid out a grim but theoretical chain of events that could have unfolded. He wrote that the sinus infection Busch had been managing could have progressed to pneumonia, then to sepsis. From there, in Morse’s telling, a blood clot lodging in the lung, a condition known as pulmonary embolism, could have led to what he described as perfusion failure or even cardiac arrest.

A commenter pushed back on the characterization, noting that a saddle pulmonary embolism and a heart attack are medically distinct events. Morse agreed with the technical correction, but stood by the severity of the scenario he described, writing, “That’s what likely killed him.”

The 911 call was placed from the General Motors Charlotte Technical Center off Speedway Boulevard in Concord, close to the Hendrick Motorsports campus. The caller described Busch as sitting on a bathroom floor, conscious but deteriorating rapidly.

“I’ve got an individual that’s short of breath, very hot, thinks he’s going to pass out, and is producing a little bit of blood, coughing up some blood,” the caller told the dispatcher, as revealed in the 911 call audio posted by TMZ Sports. Asked whether the patient was awake, the caller confirmed, “He is awake. He’s awake. He’s on the bathroom floor right now.”

The caller also requested that the responding ambulance arrive without its sirens running.

Busch Died Day After 911 Call, Six Days After His Last Win

Busch was transported to a Charlotte-area hospital, where he died Thursday, according to a joint statement from NASCAR and Richard Childress Racing. The sanctioning body described his death as the result of a “severe illness.”

The Las Vegas native was in the 22nd year of his full-time Cup career. A two-time champion — winning the Cup title in 2015 and 2019 with Joe Gibbs Racing — Busch compiled 63 Cup Series victories, ninth on the all-time list, and 234 total wins across NASCAR’s three top series.

Just six days before his death, Busch started on the pole, swept both stages, and led the most laps in a CRAFTSMAN Truck Series race at Dover Motor Speedway, claiming his 69th career Truck Series victory. Asked afterward why winning never gets old, he replied: “You never know when the last one is.”

Busch is survived by his wife, Samantha, and their two children, Brexton and Lennix. He was 41.