Southend skipper Adam Barrett has been placed on the transfer list after handing in a written request.
The 30-year-old played 41 matches for the Shrimpers last season as they were relegated from League One.
A club statement read: "The club understands the desire to play at a higher level and reluctantly agreed to allow the player to seek a new club.
"The decision to grant Adam Barrett and other senior players transfer requests has to be balanced against the wage constraints that Southend United and all clubs will operate under in League Two, which is subject to a Football League salary cap."
The news is sure to alert a number of clubs to Barrett's availability this summer.