Lockwood moved to the City Ground on a free transfer from Leyton Orient last summer, but made just 12 appearances for the club.
But he remains one of the most highly-rated full-backs in the lower divisions, having made 375 appearances in more than 10 seasons with Orient.
Colchester are looking to rebuild after finishing bottom of the Championship this season.
years.
They have already signed the defender Matt Heath from Leeds United, after the 26-year-old ended the season on loan at Layer Road.