This has put clubs in League One and the second tier needing reinforcements on red alert – especially those in need of a centre-back.
Pompey arguably fall into this category with Hayden Carter looking likely to remain at Blackburn this summer, and Sean Raggett yet to extend his stay at the Blues.
But who could they sign for free in pre-season?
Here’s who we found among the names set to leave their clubs at the end of their contracts in June.
5. Aapo Halme – Barnsley
Following his transfer from Leeds in 2019, Halme the 24-year-old has been released from Barnsley following relegation from the Championship. He made seven appearances last term, but played 20 appearances in their run to the play-offs last season. Picture: George Wood/Getty Images Photo: George Wood
6. Cyrus Christie – Fulham
Shortly after his loan deal from Swansea ended, Christie was released by the Premier League new boys. He is conventionally a right-back, but is no stranger to centre-back and at 29-years-old, still has a lot of football in him. Picture: Mark Thompson/Getty Images Photo: Mark Thompson
7. Sol Bamba – Middlesbrough
Bamba, rightly, received applause for successfully beating cancer to return to Championship football at Middlesbrough. Last season he made 29 appearances but at 37-years-old, maybe looking at retirement. Picture: Stu Forster/Getty Images Photo: Stu Forster
8. Alex Pearce – Millwall
After 81 appearances for Millwall, Alex Pearce’s time in London has come to an end. Another experienced option for League One clubs at 33-years-old. Picture: Alex Burstow/Getty Images Photo: Alex Burstow