Goalkeeper Ben Williams is leaving Colchester United after turning down the offer of a new contract.
The 29-year-old former Manchester United trainee made more than 120 appearances for the club after joining them from Crewe in 2009.
"Ben wants to play in the Championship and feels now is his best opportunity," boss John Ward told the club's website.
"We gave him quite a lot of leeway in terms of his new contract, but we have to respect the decision he's made."
Ward confirmed that Williams' understudy Mark Cousins, 25, would be his first-choice keeper next season.
"He has improved all the time I've been here, he works extremely hard and I'm pleased for him that he's now going to get this opportunity," he added.