Franklin County Coroner Jan Gorniak said toxicology tests will not be finalized for four to six weeks.
"It's leaning toward an apparent natural death, but we don't know why," Gorniak said.
She said the autopsy revealed no trauma to Urso's body, along with no blood clots. In addition to toxicology tests, the coroner's office will also take a closer look at what Gorniak referred to as "heart changes."
"What that means is we saw some changes with his heart but we don't know what it is until we examine it underneath the microscope," she said. "So it could be something or it could be nothing. But it's not definitive as a cause of death right now."
Urso played in six games with the Crew and was rehabbing from a sports-groin injury sustained in May. He did not travel to the game at D.C. United on Saturday night.
In a 9-1-1 call provided by police to The Columbus Dispatch, an unidentified female says, "Officers are with him. It's a very drunk person who fell down and now he's unconscious."
It is unclear if the speaker is affiliated with police, fire or an emergency crew or if she is a bystander.
Major League Soccer observed a moment of silence at both of its games on Sunday.
"We are deeply saddened by the death of Columbus Crew player Kirk Urso," MLS Commissioner Don Garber said in a statement. "Major League Soccer mourns his death and sends our condolences to his family."
Urso, an Illinois native, played for and was the captain at North Carolina last fall when it won the NCAA championship.
On the Tar Heels soccer team's website, North Carolina athletic director Bubba Cunningham said Urso's former teammates and friends were devastated by the news of his death.
"In the very brief time I spent with Kirk it became evident that he was a natural leader," Cunningham said. "His enthusiasm was contagious to all who knew him. He had a positive and inspirational impact on his team, and many other student-athletes at Carolina."
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