Neil McRoberts is insisting Portsmouth clean up their act for Saturday’s London three south west trip to Old Georgians (2.30pm).
The senior coach has been dismayed by the lack of discipline shown in recent weeks.
In their past two games they have conceded more than 50 penalties.
At the same time they have also been collecting yellow and red cards.
Against both Andover in the league and Bromley in the cup Portsmouth finished the game with just 13 players on the pitch.
The Rugby Camp side won both games but McRoberts feels their luck will run out at some stage.
The Portsmouth coach said: ‘If we can't keep 15 players on the pitch it will be a recipe for disaster.
‘It is frustrating because it is the same infringements time and time again.
‘The players are not learning from it.
‘We have said to them what needed to be said this week and it has been made perfectly clear what is expected of them.
‘The present situation is not sustainable.
‘So far our structures have got us through but that won't always happen.
‘As a team you are bound to concede some penalties and get some cards.
‘It is the daft ones we need to cut out otherwise it is going to hurt us.’
Despite the problems Portsmouth are second in the league and are on track to achieve their promotion ambitions.
McRoberts believes the next three games will have a crucial bearing on how the season will pan out.
In the next two weeks they take on promotion-rivals Battersea Ironsides and Winchester.
Apart from that they are also still on the Twickenham trail in the RFU Senior Vase.
Improved discipline is essential if the club are to progress on both fronts.
In the 24-10 Vase win against Bromley Portsmouth showed they are a very dangerous outfit when they are focused.
McRoberts added: ‘We have a big powerful, physical, abrasive pack of forwards who can take charge of games.
‘They are capable of providing a platform for us to win games.
‘When our three-quarters are given ball in space they are devastating with their pace.
‘They are capable of cutting our opponents apart.
‘We need to make sure we make the most of our talents.
‘Now we have an important period coming up before Christmas.
‘At the end of it we will either put ourselves into a good position or leave ourselves with a tough task.’
The visitors are boosted by the return of captain Daz Leggatt in the pack and Fijian Sully Cau Cau on the wing.
Luke Peters also returns from international duty with Cyprus.
Tim Snowdon reverts to the back row with Elliott Worrall coming in at number eight.