Lokeren defender Gregory Mertens remained in critical condition on Wednesday, two days after he suffered heart failure during a training match.

The 24-year-old player in Belgium's top division collapsed early in Monday's game, and has been kept in a coma as doctors continue to give him emergency treatment.

Lokeren team doctor Kris Peeters told VTM network that "a few problems arose" during operations on Tuesday: "We only know they are doing their utmost to turn things around. But we all heard things are not going well."

The club said he had been medically screened several times during his career, and that nothing pointed toward a fundamental heart problem.