I'm honestly not worried about the results or the fitness levels. Slogging in matches you lose probably builds stamina a lot better than cruising through easy wins. Martinez is a licensed physio remember so fitness isn't something I'm thinking about.
The only concern for me is the state of the World Cup players but don't forget, everyone else in the league will be in the same boat if not worse off, especially our nearest competitors.
Of course we'd all like an ideal pre-season where we score for fun, Lukaku slots loads, Baines hits loads of free kicks etc, but if we beat Leicester who have won 6 out of 6 in a scruffy 1-0 then none of it will be a problem.