Gregory Mertens (2 February 1991 – 30 April 2015) was a Belgian professional football player. His usual position was central defender. He began his senior career with Cercle Brugge and was under contract with Lokeren before he suffered a fatal cardiac arrest during a reserve game in 2015.

Mertens moved from the reserves of K.A.A. Gent to the first team of Cercle Brugge in the 2010–11 winter transfer window, at the recommendation of manager Bob Peeters, who had been his coach at the Gent reserves the previous season.

On 12 February 2011, Mertens made his senior debut for Cercle as an 89th-minute substitute for Hans Cornelis in a match against his former team R.S.C. Anderlecht. Cercle lost the match 1–0.

On 23 May 2013, he scored his first hat trick against WS Woluwe.^{[citation needed]}

Mertens suffered a cardiac arrest during a reserve game for Lokeren against K.R.C. Genk on 27 April 2015. He was immediately taken to hospital where he was put in an artificially induced coma.^[1] He died on 30 April 2015 at around 16:30. Lokeren declared that Mertens had passed all fitness tests set by UEFA, and therefore the cause of his cardiac arrest needed to be established.^[2]

On the day after his death, Lokeren lined up for their play-off match against Westerlo in T-shirts bearing Mertens' name and squad number 4.^[3]

Lokeren

• Belgian Cup: 2013–14^[4]

• List of association footballers who died while playing
• List of association footballers who died during their careers