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.
9. Paul Huntington – Preston
Huntington’s time at Preston has come to an end after 10 years at Deepdale. In that time, he made 306 appearances for the club and saw their rise back to the Championship. Knows how to get promoted. Picture: Dan Mullan/Getty Images Photo: Dan Mullan
10. Dominic Ball – QPR
Conventionally a defensive-midfielder, Ball has often operated at centre-back. At 26-years-old will tick a number of boxes for clubs in the Championship and League One. Last season he scored once and made 23 appearances under Mark Warburton. Picture: Jacques Feeney/Getty Images Photo: Jacques Feeney
11. Michael Morrison – Reading (in talks over new deal)
At present, the defender is yet to sign a new deal with the club, but is in talks with the Royals over extending his stay. It’s clear to see why as he made 29 appearances on their way to survival. Picture: Naomi Baker/Getty Images Photo: Naomi Baker
12. Timm Klose – Bristol City (in talks over new deal)
Similar to Morrison, Klose remains in talks over a new deal with his current employers. If he fails to do so, the man who featured in the Premier League for Norwich could add vital expertise to a League One club’s backline. Picture: Harry Trump/Getty Images Photo: Harry Trump