The Croatian was back on the scoresheet in victory over Sunderland on Saturday.
"It makes a huge difference. He has not scored in his last few games and he'll have be disappointed with that," said Naismith.
"He's not had many great chances in the game but the one that came his way he was composed and he put it away in the corner and that is why he has such a big reputation.
"Going forward Fellaini has probably been our most prolific and even Kevin Mirallas, in the last few games, has been very direct and arguably our most influential player.
"It is down to the quality we have in the squad. We are happy with the boys we've got and that is why we are pushing for the top spots."