People saying Barkley in Naismith out right away, this would be awful man management from Martinez if he was to do this. Basically saying however well you play and however many goals you score you'll just be dumped out the team as soon as an injured player is back. If he wants to change the style to accommodate the pair then I'd go:
Barry
Besic McCarthy
Barkley
Naismith Lukaku
However, if he's going to keep the same style I'd just play Naismith behind Lukaku. Barkley's a fantastic player but everything else can't be dropped and switched around just to accommodate him in the team, that's the way players get too big headed at a young age. Personally; I'd have them both in the team in the way I said, but Barkley should have to fight for a place if the style isn't to be changed.