The home match between Dinamo and Viitorul was at 3-3 and being broadcast live when midfielder Ekeng fell to the ground in the 69th minute, seven minutes after he went on as a substitute. Local media reports said he had a heart attack.
The game was stopped and the 26-year-old Ekeng, from Cameroon, was immediately taken to Floreasca Emergency Hospital. Dozens of fans gathered outside the hospital.
Players and staff could be seen crying as events unfolded. Some went with him to the hospital.
He has played for Spanish club Cordoba CF, Swiss club Lausanne, and French club Le Mans. He moved to Dinamo in 2015.