The former Olympiakos striker has made just one start since his January arrival from Olympiakos.
Heitinga told the Fulham Chronicle: "Kostas has his first start under his belt, and hopefully he can score some goals for us now.
"Obviously he was injured, and he came from Greece, where he was used to playing for trophies and for the Champions League spots - this is very different for him.
"But this is a trophy too, to stay up. It's the same now as winning a cup or a title. This is the best league in the world and everyone wants to be in it.
"We need to change something and it needs to be quick, as time is running out now, but there's 20 still points still to fight for.
"You don't want to be in a situation like this, but you need to handle it as a group. We need to stick together as a team, and we need to have a little bit of luck.
"We have got the quality in the squad, but we need to show it on the pitch."
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