The Croatia international striker has netted just two goals in 19 games for the Toffees, a disappointing run of form that is in stark contrast to last season's goalscoring heroics.
And Moyes admits it could require a change of fortunes for the man signed last season from Rangers if his side are to secure UEFA Champions League qualification this season.
"If he fires and scores, we can have a strong end to the season - and it could get us into the top four," said Moyes.
"Last year, at this time, nearly everything he touched went into the net.
"That could be the key for us, because how we finish the season will depend a lot on how Nikica Jelavic performs."