The Italian boss has had his side doing double training sessions since early July after only narrowly avoiding relegation last campaign.
And Johnson insisted that, although it has been tough, he and his team-mates are ready for a much improved campaign this time around.
"We had an idea towards the end of last season that pre-season was going to be hard under the new manager," Johnson is quoted in the Daily Star.
"I think we're looking fit and strong right now.
"There's a quiet confidence growing in the squad and a much better idea of what is expected of us."