Sunday’s 1-0 win over Russia saw the Red Devils tighten their grip on first place in Group H, with a place in the last 16 firmly in their sights.
Nacer, who played in Belgium’s 2-1 victory against Algeria in their first match of the tournament, knows his nation is in an advantageous position heading into Thursday’s 9pm kick-off against a South Korea side currently propping up the group standings.
But he confirmed there will be no let-up from his country as they seek to build momentum to carry into the knockout stages.
“South Korea are always there when it comes to World Cups,” said the 24-year-old, who is joined in Belgium’s squad by Spurs team-mates Jan Vertonghen and Mousa Dembele.
“I think they’re a good team and they play a different kind of football than the Europeans – they are strong as well.
“We know they can play good football so we cannot and will not underestimate them. Like I’ve said before, we have to be at 100 per cent against every team.”