Dion Donohue will leave Pompey at the season’s end.
The Blues have decided against activating a 12-month option to extend the midfielder’s Fratton Park stay.
It means Donohue will next month depart upon the expiry of his existing two-year deal.
Kenny Jackett had been keen to retain the talented 25-year-old, yet ultimately the Welshman’s persistent injury problems forced the manager’s hand.
Donohue featured just 13 appearances this season, the last of which was a substitute outing against Scunthorpe in March.
He is currently unavailable for Thursday’s League One play-off semi-final second leg with Sunderland through a groin complaint.
Signed by Jackett from Chesterfield for an undisclosed fee in August 2017, Donohue demonstrated his versatility during two Fratton Park seasons.
Primarily a midfielder, he largely served the Blues at left-back, adjusting impressively to finish the 2017-18 campaign strongly.
He was earmarked for his favoured central-midfield role this season, yet a succession of illness and injury problems hampered his availability.
Donohue netted a maiden Pompey goal upon his first-team comeback at Crawley in the Checkatrade Trophy in October, proving to be the match winner.
Yet, after re-establishing himself in the first-team as a midfielder for four-successive matches, once again injury intervened.
Memorably, it was Donohue’s wonderful pass which created Andre Green’s dramatic winner at Norwich in January’s FA Cup encounter.
However, he would make just eight more appearances during the remainder of the campaign.
Donohue totalled 48 games and one goal during a two-year Pompey spell which is now at an end.
Also out of contract this summer are Nathan Thompson, Matt Casey and Dan Smith.