The Everton forward has hit a rich vein of form with six goals in his last five matches for club and country, with the Merseyside club moving into contention for the top four.
The 23-year-old is being linked with a move away from Goodison Park after rejecting the club’s latest contract offer, with talk of a £70m return to Chelsea cropping up this week, but the club appear relaxed on his future.
Even though they beat Arsenal earlier in the season, Lukaku was not able to get himself on the scoresheet against the Gunners, and he revealed to former Liverpool defender Jamie Carragher in an interview for Sky Sports that going up against Koscielny has proven his toughest test this season.
"Koscielny I think is really good,” said Lukaku. “Every time when I played against Arsenal... he's not the biggest but I think he's got the brains.
"I've been in this league since 2011. Every time when I played against him, my hardest games were against him, because he's so clever."
Everton travel to the Emirates Stadium on the final weekend of the season, where a top four finish could be on the line given that both sides are in the mix for European qualification.