The 32-year-old started for the U's against Sheffield United on Saturday having just returned for a second loan spell with the club on Friday.
With fellow forwards Deane Smalley and Jon-Paul Pittman still sidelined and Constable suspended, the Burton forward is set to continue alongside Tom Craddock at the Kassam.
But one new signing who will not feature against Southend is loanee Lewis Montrose who is cup-tied having already featured in the competition for parent club Gillingham this season.
Manager Chris Wilder is unlikely to make too many changes to his side but could recall Michael Raynes in the heart of defence and rest Michael Dubbery.
"We've just got to go and not get knocked out of two cup competitions in the space of a week," he told the Oxford Mail.