David Moyes is hoping Aiyegbeni Yakubu's goals will prove crucial in Everton's bid to secure a Champions League spot.
Four goals in his last two games have taken the 25-year-old's tally to 16 goals in all competitions so far this season.
Moyes has challenged Yakubu to become the first striker at Goodison Park to hit 20 top-flight goals since Gary Lineker 22 years ago.
Everton face Yakubu's former club Portsmouth at Goodison on Sunday and Moyes is confident he will score more goals.
"He has made a difference because he has added more goals to us," said Moyes.
"But importantly his play has improved since he has come here as well. He is enjoying his time, we need him and his goals have become a big factor.
"I always thought that anybody that comes to Everton, part and parcel of the job is that you have to fit into the work environment - from my point of view I think he has."
Everton splashed out over £11million to land Yakubu from Middlesbrough in the summer after failing to qualify for the Champions League last season.
Moyes revealed he is pleased with the performances of the Nigeria international and is not surprised that their record signing has impressed.
"Previously we relied heavily on Andy (Johnson) and on Tim Cahill for our goals," he added.
"I knew when we brought him in if he scored the goals here he had at his other clubs that would add to our goal total come the end of the season. That has proved to be the case.
"If he could get 20 league goals for us, that would be absolutely tremendous.
"He is always looking to improve his tally, which every good forward should do, and hopefully he will get a few more for us."