Turnbull, who was withdrawn from the reserve-team squad for Wednesday night's trip to Bolton, is in line to make his third senior appearance for the club after playing eight games on loan at Cardiff earlier this season.
Southgate said: "To be honest, we are getting quite used to it. People say we are having no luck, but we are - it is just it is all bad.
"We have to get on with it. It is a great opportunity for Ross Turnbull, with Mark getting his injury.
"He is really looking forward to the chance."