Jelavic is mired in a dreadful run of form which has seen him score just once (on March 16) in his past 25 matches for the Toffees.
"Niki has been working extremely hard and he should not be judged by the number of goals he has scored," said Martinez.
"If you look at the goal we scored against Chelsea it was a perfect header (by Jelavic) back into the six-yard area so his contribution was perfect on the day and it is about maintaining standards on the day.
"Every player wants to have as strong a squad as you can have because the competition is really demanding and you want to look around and see players that you know if you drop your standards you will lose your place to.
"Everyone is in that frame of mind. You want to be at your best, knowing you can help your team."