Portsmouth chief executive Mark Catlin admits the club could face a fine after a flare was let off during Saturday's 1-1 draw with Sunderland.
The Football Association are set to investigate the incident, which saw the device end up among Sunderland fans in the family section.
The Black Cats' promotion rivals are bracing themselves for a fine, although they are not expecting any points deduction as a result of the incident which followed Jamal Lowe's first-half equaliser.
Northumbria Police confirmed a Portsmouth fan was arrested Portsmouth fan arrested after flare thrown into Sunderland end during League One clash - and it's not the first time Pompey fans have set off such devices this season.
It is a criminal offence to take smoke bombs or flares into a football ground in the UK, and Catlin has stressed again the club's stance on the matter.
"As part of the Chairman’s Charter and under stadium safety and security rules, pyrotechnics are not permitted within a stadium," told the Portsmouth News .
"We couldn't have made that any clearer to our supporters – the use of pyrotechnics are just not acceptable any more.
"We’ve had various reports of some people either hit by flares or succumbing to inhalation of the smoke from the canisters.
"Just because a few think they improve the atmosphere, that shouldn’t stop others being able to enjoy a game in a safe and secure environment without fear of choking on the smoke or actually getting hit by the flares.
"We are still investigating reports that a young person was hit and hurt at Sunderland. It is something we are trying to verify.
"However, currently in the UK, under every single rule book, pyrotechnics are not allowed into stadiums.
"I would like to stress, these are not our rules, these are national rules which have to be enforced by various bodies and the law of the land. These must be adhered to and, as a responsible football club, we have to uphold that policy.
"The FA will conduct an investigation and then it is at their discretion whether we are fined or not. I am convinced there will be an investigation for this one, it is quite high profile.
"There’s a wide range of punishments available. Personally, I have never known a club docked points for the discharge of a pyrotechnic – but potentially there could be a fine.
"We’ve had quite a few instances this season. Regulatory bodies will look at our record and, unfortunately, it’s not great."
Portsmouth fan arrested after flare thrown into Sunderland end during League One clash
