Niasse 's arrival has put Romelu Lukaku 's long - term Everton future in doubt .
Martinez insists Niasse brought the Moscow man in to boost Everton 's forward line -- and not with a view to Everton 's their top scorer .
Niasse 's arrival has put Romelu Lukaku 's long - term Everton future in doubt but Martinez insists he brought the Moscow man in to boost their forward line -- and not with a view to replacing their top scorer .