(CNN)A Belgian footballer remains in critical condition after collapsing on the field of play with doctors admitting his situation "doesn't look very good."
Gregory Mertens, who plays for Lokeren in his home country, was given cardiopulmonary resuscitation (CPR) during Monday's reserve game with Genk after falling to the ground with a heart-related illness.
Mertens, 24, has been in an induced coma on a life support machine since the incident.
"He's not getting better and his condition will not improve in a couple of hours or in a day," a spokesman for Genk hospital told CNN
According to Lokeren's club doctor, Kris Peeters, Mertens suffered heart failure, though the exact cause remains unknown.
He said that Mertens was an "elite sportsman" and that the situation was a "very difficult thing to accept and understand for many people."
European governing body Uefa introduced mandatory cardiac testing for all players taking part in its competition in 2008 following the deaths of Marc-Vivien Foé, Antonio Puerta and Phil O'Donnell.