The full-back, who the Blues have identified as a potential replacement for Cam Pring, was not included in manager Aitor Karanka’s plans for the lunch-time game at the Riverside, despite being allowed to name nine substitutes.
Seddon is yet to feature for his parent club after having his loan spell at Wimbledon cut short on the eve of the January transfer window.
He was recalled to help Brum deal with injuries, but remains without a game since the Dons’ 2-0 defeat at Oxford on Boxing Day.
The 23-year-old made 19 appearances for Wimbledon over the first four months of the season.
Yet a place on the bench for Birmingham’s 2-0 defeat at the hands of Blackburn on January 2 is all he has to show following his St Andrew’s return.
Pompey are keen on Seddon returning to Fratton Park, after a successful loan spell over the second half of last season.
They need reinforcements at left-back after Bristol City recalled Pring early from his PO4 loan spell.
Last week, The News revealed that the Blues’ feared their chances of landing Seddon were diminishing.
Pompey have since been linked with a move for Shrewsbury’s Charlie Daniels.
But today’s developments from Birmingham could pave the way for some moment.