Lukaku has been in fine form for Everton this season and had scored 21 goals and made six assists in 28 games heading into this weekend’s round of games.
The Belgian forward has established himself as one of the top strikers in the Premier League under Ronald Koeman so far this term.
Koscielny, meanwhile, is widely regarded as one of the Premier League’s strongest defenders, despite Arsenal’s disappointing form in recent weeks.
And Lukaku says that he considers Koscielny to be one of the toughest defenders he has ever faced in his career.
Speaking in an interview with Sky Sports before Saturday’s Merseyside derby, Lukaku said: “Koscielny I think is really good, every time I’ve 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 I played against him, the hardest games were against him because he’s so clever.”
Koscielny will be hoping to feature for Arsenal when the Gunners take on Manchester City in the Premier League at The Emirates on Sunday afternoon.
The north London side are desperately looking for a victory to get their top-four bid back on track.
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