Delta's Henry Chinonso Ihelewere, 21, collapsed with no-one around him only 15 minutes after coming on as a second-half substitute.
He was taken to hospital but he never regained consciousness.
The striker had been playing in Romania since 2007 when he joined Farul Constanta.
"What can I say? We're all shocked," Universitatea Cluj boss Cristian Dulca, who previously coached the Nigerian, was quoted as saying. "It's a tragic day for Romanian football.
"I trained him for a year and a half and I can tell you he was a real example in training. He could've become a very good player."
Urso, who played six games for Colombus this season before picking up an injury, was pronounced dead at Grant Medical Center in Columbus this morning.
No further details were given of the cause of death, although it has been widely reported that uniformed police officers were called to a bar in the city an hour before he died in hospital. It is believed Urso had collapsed.
The North Carolina graduate was in his first year as a professional.