The former Fulham striker signed for West Ham last week.
"(Petric) has been training with us but obviously he is a bit behind because he hasn't had a full pre-season.
"He's in great shape coming back, don't get me wrong, but it's just football fitness. He has got to get used to that and hopefully we will have him there or thereabouts for Everton, maybe to come off the bench.
"It is a great acquisition for us - we are very pleased we have got him. He brings a lot of quality and something different. He is another one that we have got to get used to."
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