The 24-year-old defender had been in a critical condition after collapsing on the field 20 minutes into a reserve game against Genk on Monday.
He was given emergency treatment on the pitch before being taken to hospital where he was placed in an induced coma.
Lokeren described Mertens as "modest" and "indispensable".
"Suddenly something happens which makes us realize that football is just football. Today is such a time," said a statement by the club.
Mertens began his career at the country's most successful club, Anderlecht, but moved to Lokeren in January last year from Cercle Bruges.
He had been capped several times by Belgium at under-21 level.
Belgium suffered the loss of another young talent in January this year when 20-year-old Junior Malanda of German Bundesliga side Wolfsburg died in a car crash.
You’ve reached your limit of {{free_limit}} free articles this month.
Subscribe now for unlimited access.
Already subscribed? Log in
Subscribe to read the full story →
Smart Quarterly
₹900
3 Months
₹300/Month
Smart Essential
₹2,700
1 Year
₹225/Month
Super Saver
₹3,900
2 Years
₹162/Month
Renews automatically, cancel anytime
Here’s what’s included in our digital subscription plans
Exclusive premium stories online
Over 30 premium stories daily, handpicked by our editors


Complimentary Access to The New York Times
News, Games, Cooking, Audio, Wirecutter & The Athletic
Business Standard Epaper
Digital replica of our daily newspaper — with options to read, save, and share


Curated Newsletters
Insights on markets, finance, politics, tech, and more delivered to your inbox
Market Analysis & Investment Insights
In-depth market analysis & insights with access to The Smart Investor


Archives
Repository of articles and publications dating back to 1997
Ad-free Reading
Uninterrupted reading experience with no advertisements


Seamless Access Across All Devices
Access Business Standard across devices — mobile, tablet, or PC, via web or app
