With Heynen now appointed captain by Mazzu, he featured in Genk's early UEFA Champions League exit in 2019-20 having been paired with Liverpool, Napoli and a Salzburg side containing Erling Haaland and Takumi Minamino.
[6][7][8] After a disappointing campaign the following season where defensive frailty saw van den Brom dismissed mid-season, and Bernd Storck only able to guide Genk to the 2022 Belgian Pro League's European play-offs, Heynen's form surged under the tenureship of new coach Wouter Vrancken.
[9][10] Heynen was named by Belgium national team coach Roberto Martinez in the preliminary Belgian squad of 55 ahead of the 2022 FIFA World Cup, but didn't make the plane for Qatar.
A continuation in strong form saw big calls for Heynen and team-mate Mike Trésor to be capped by new national team coach Domenico Tedesco for his first games in charge against Sweden and Germany in March 2023,[11] but neither player was chosen.
[12][13][14][15] Heynen battled through a muscle injury to score a late equaliser away to KVC Westerlo to squeeze Genk into the 2023-24 title play-offs, but the damage inflicted ruled him out for the rest of the season.