Captain Barker, who has only recently returned from a calf injury, was forced off in the first half of Saturday's 2-1 win at Wycombe nursing an Achilles problem and will be checked over.
As will midfielders Leonard and Reeves after they both picked up knocks at the weekend.
Manager Paul Sturrock is already without Mark Phillips (broken toe), Marc Laird, Caolan Lavery (both hamstring), Gavin Tomlin (thigh), Michael Timlin (broken leg) and Bilel Mohsni (suspension).
The Shrimpers currently find themselves just two points outside the play-off places and six adrift of the top three as they make the short trip to Underhill.
- Sports & Recreation
- Gavin Tomlin
- Mark Phillips