Pompey have lodged an appeal against Gareth Evans’ Abbey Stadium red card.
The midfielder was dismissed in stoppage-time during Saturday’s 3-1 win following a late challenge on Elliot Omozusi.
The Football Association subsequently issued a three-match ban on the basis of serious foul play.
However, the Blues have now appealed against referee Seb Stockbridge’s decision.
Having studied video footage of the incident, the club believe they possess a genuine case to reduce Evans’ suspension.
That centres on the ex-Fleetwood player’s foot pointing downwards and almost planted on the floor at the time of the mistimed tackle.
In doing so, the club argues the foot was not high and contradicts match official claims that Omozusi was struck on the shinpad.
However, Pompey accept the incident was a foul by Evans.
The Blues are now awaiting the appeal outcome.