The Hawks are in the bottom four after winning promotion to Non-League football’s top tier for the first time last season.
But it hasn’t gone totally to plan and they face a return to the National League South unless results pick up.
The south coast club have not tasted victory in seven games but they face out-of-form Maidstone United this weekend.
Bradbury has spoken to the Portsmouth News and says it’s crunch time for the club - and has backed his team to get enough points to keep them in the division.
“The next ten games are probably the biggest in the club's history,” the manager said.
“If we continue playing with the same desire, work rate and intent that we have recently then we will be good enough.
“We have worked hard to get where we are and are determined to stay there.
“The players are determined to give it everything they have got. Whatever happens it won't be for a lack of effort. We are focused on staying up.”