The French striker has scored eight times for the Ladbrokes Premiership champions in 14 games this season.
Nicholas thinks he could be doing more in order to live up to his potential and become a £25 million striker.
He said to the Daily Express: "Odsonne Edouard is the top striker in Scotland but Alfredo Morelos is starting to close the gap.
"The Celtic frontman is a better all-round footballer, although he has this slightly annoying habit of looking too casual and uninterested a lot of the time.
"It's as if he can't be too fussed in the so-called lesser games. The thing that irritates me more than anything is his lack of celebration when he scores. It should be the greatest feeling in the world but Odsonne doesn't show that.
"The Frenchman has shone on the big stage and he has a growing composure in front of goal.
"People are already saying he is better than Moussa Dembele, who left for £20m but I'm not so sure. For me, Dembele has more cunning and aggression in his game. However, I can see Edouard continuing to improve and leaving Celtic in a year or so for at least £25m.
"Edouard and Morelos are top-class players and we should cherish them while they're in the Premiership."