Will Knight expects Havant to be on top of their game against Hove in their re-arranged London one south clash at Hooks Lane.
Havant – without a win since Christmas – have slipped into the relegation battle and need to turn the corner.
Knight was disappointed by the performance in last week’s defeat at Cobham and wants to see a big improvement.
‘We have to step up our game,’ said Havant’s head coach. ‘It has got to the point where we can’t afford to slip up because Gosport & Fareham are breathing down our necks.
‘If we win and they lose then we can open up a gap between us but if the opposite happens then it will give them an advantage.
‘This is a defining weekend for both teams.
‘Last week we didn’t do the job so we have to go all out to get a result in this game.’
The home side are hit by the absence of two key players in their three-quarters.
Captain Joel Knight is in action with the Welsh Students Rugby League squad and leading try-scorer Loz Blackburn has Navy duties.
Havant will reorganise in the backs with Sam Berridge and James Read forming the centre partnership and Ed Wilks in on the wing.
Knight is boosted by the return of wing-forwards Jim White, from injury and Dom Bellman, from Army duties.
‘The message to the players this week has been the need to establish a platform for our talented backs,’ said Knight.
‘We have a couple of key players missing but can’t use that as an excuse because the players coming in are more than capable of doing the job.’
Havant: Doe, J Blackburn, Berridge, Read, Wilks, Living, Davenport, Rubenheimer, White, Bellman, Roberts, Parkins, Ward-Golden, Elsmore, Osbourne, Powell, Anchor, Morris.