The Football Association have written to Pompey asking for their observations on Saturday’s pitch invasion.
Around 200 Blues supporters left the stands and went on to the Griffin Park playing surface following the 3-2 defeat for Guy Whittingham’s men.
The FA have acknowledged there was no violence attached to the invasion.
However, pitch encroachment is an offence and clubs can be fined.
Pompey feel they have mitigating circumstances which should be taken into account and are hopeful they can avoid punishment.
They will point to it being the end of an emotional week for fans, who saw the near-completion of a community bid.
In addition, it was Brentford’s responsibility for policing and stewarding as the home club.
Pompey will also explain tickets were sold to only season-ticket holders, with none going on general sale because of the early demand.
And backed by the knowledge Blues fans have behaved themselves during this season, it is hoped there will no punishment.
A Pompey spokesman said: ‘We are continuing to liaise with Brentford and have had communication from the Football Association.
‘They have asked for our observations, which we are responding to once we have all the facts.
‘This will be done within the next week. In a situation like this, you also liaise with the home club and look at measures that were taken and go through the correct process.
‘Going on the pitch is an offence but it was a dizzy day for everyone.
‘Reasonable action in the build-up was also taken and there was nothing to suggest this would be classified highly.
‘And there is certainly no history of trouble between the clubs.’
In the aftermath of the pitch invasion, owners-in-waiting, the Pompey Supporters’ Trust, have urged fans not to repeat their actions.
A potential club fine could result in crucial Trust funds being used to settle such a debt.
However, at present that is too early to call as both Pompey and the FA look into matters before an official conclusion can be reached.
The Blues have two matches remaining this season.