Belgian defender Gregory Mertens has shown no signs of improvement and remains critical in hospital after he collapsed with a heart-related illness.
The 24-year-old Lokeren player was given CPR in the first half of Monday's reserve-team game with Genk.
But he remains in an induced coma on a life support machine, with a club spokesman saying on Wednesday: "We are waiting for the worst news to come."
Lokeren's Pro League game with Westerlo will go ahead on Friday.
Discussions were held between the two clubs and the Belgian league as to whether the game should be cancelled.
But with the duration of Mertens's condition unknown, it was thought best to continue with the league programme despite the sombre mood at the club.
The fixture is Lokeren's penultimate match of the season.
Lokeren say that the exact nature of Mertens's heart condition has yet to be established.
They added that he passed all the pre-season health tests required by Europe's football governing body Uefa and was judged to be one of the fittest players at the club.
A former Belgium Under-21 international, Mertens joined Lokeren in the summer from Cercle Brugge and has played in 15 league games this term, as well as against Hull City in the Europa League in August.
Monday's game was postponed while Mertens was being treated.
And the former Chelsea midfielder Kevin De Bruyne tweeted: "Incredibly bad news. Keep fighting Gregory."