mahon was without a club for the first two months of the 2013–14 campaign, eventually signing for league two side portsmouth on a one-month deal on 4 october 2013. he made his portsmouth debut four days after signing, playing the whole match in a 2–1 football league trophy away win at oxford united. mahon was sent-off in a 2–1 loss to former club stevenage in an fa cup tie on 9 november 2013, receiving a straight red card for an elbow on filipe morais. he made three appearances in total during his brief spell at portsmouth, leaving upon the expiry of his contract on 28 november 2013.<ref name="games played by gavin mahon in 2013/2014"></ref>