Kenny Jackett left the decision to release Dion Donohue as late a possible but admitted: Injuries cost him.
The Welshman has been released by Pompey after the club decided not to take up the option of an additional 12 months on his two-year contract.
The 2017 summer arrival from Chesterfield was held in high regard by the Blues boss and his team-mates.
After an encouraging maiden season – operating mainly as a left-back – Donohue’s second campaign at Fratton Park was ravaged by various injuries.
Earmarked to play a prominent role in central midfield, the 25-year-old made just 13 appearances during the failed League One promotion push.
Jackett revealed he delayed his decision on Donohue’s future for as long as he could.
But the cultured left-footer’s setbacks meant the Pompey boss couldn't extend his stay.
Jackett said: ‘Dion is a really talented player. Certainly in his first season he showed a flexibility down the left-hand side.
‘We felt he could really settle into that central-midfield role this season and give us a range of passing, which at times we haven’t had.
‘Ultimately, injuries cost him. Even in the last month of the season, he had two groin injuries.
‘We were hoping he’d perhaps get back for the Sunderland play-off game when Lee Brown and Brandon Haunstrup were out.
‘His preferred position was central midfield and that didn’t quite happen this season.
‘Ultimately, because of that, we have decided to let him go.
‘There’s some frustration this year about not getting him out on the pitch more.
‘We left the decision open right to the end, definitely.
‘Even then I was open. Anton Walkes did a fine job (at Sunderland) but even in the second-last game of the season at the Stadium of Light he would have played.
‘Late in the game, he could have even came on and put a few crosses in.
‘It’s something I wanted to keep open because there was so much riding on the season.
‘I was open-minded right to the end. Then, ultimately, perhaps a fresh start might be best for him.’
Jackett pinpointed Donohue’s performance at Norwich in the 1-0 FA Cup third-round victory as a reason why he delayed his decision.
The boss added: 'It was a tough call when someone has had the injuries he’s had this season because somewhere along the line he can come through it.
‘I think he’s a very talented player – look at his game at Norwich.
‘He came out of nowhere to play left-back when Brown was out with a hamstring injury.
‘He had a terrific game there and then you go back to the season before.
‘I always felt who could go into the holding-midfield role but he couldn't quite get going and we wish him all the best.’