Christian Eriksen was "gone" before he was resuscitated after suffering a cardiac arrest, the team's doctor, Morten Boesen, said in a news conference Sunday.
Eriksen is in stable condition after being taken to a hospital in Copenhagen after he collapsed on the pitch.
"He was gone, and we did cardiac resuscitation. It was a cardiac arrest," Boesen said. "How close were we [to losing Eriksen]? I don't know.
"We got him back after one defibrillator, so that's quite fast. I'm not a cardiologist, so the details I will leave to the experts at the hospital."
Eriksen had just played a short pass when he fell facedown onto the ground and was given urgent medical attention for around 10 minutes.