Autopsy results show a University of Central Florida football player who died after spring drills had a pre-existing medical condition worsened by physical stress.

The Orange County Medical Examiner’s Office said Thursday that Ereck Plancher had a sickle cell trait that caused problems with his red blood cells during physical exertion. Tests showed the blood flow to the 19-year-old wide receiver’s muscles and organs slowed or stopped.

Plancher collapsed in March, the day before spring practice was to begin. UCF says he received CPR from trainers and was rushed to a hospital, where he was pronounced dead.