Campbell suing Portsmouth for unpaid bonuses
"It's being handled by our lawyers," a club spokesman said on Wednesday.
The Daily Telegraph newspaper said former England player Campbell, now back at Arsenal, was claiming 1.7 million pounds in allegedly unpaid image rights fees and bonuses plus interest.
It said the claim was detailed in a writ lodged in the High Court.
On Tuesday Portsmouth moved a step closer to becoming the first Premier League club to enter administration when their attempt to have a winding-up order struck out was dismissed by a High Court judge.
The south coast club, owned by Saudi businessman Ali al Faraj, had argued the Value Added Tax (VAT) portion of their outstanding tax bill was too high by 7.5 million pounds.
Bottom of the league Portsmouth have been banned from any transfer activity and have three times failed to pay their players on time.
Last week the Premier League awarded seven million pounds of their television revenue payments to other clubs who were still owed transfer fees by Portsmouth.