The 37-year-old was taken off after just 21 minutes of the 1-1 draw with Burton with a hamstring injury and he confirmed on Twitter that he expects to be out for between two to three weeks.
He was replaced by Tuesday night by Michael Raynes and the centre-back could get the nod from the start at Roots Hall.
The club will also assess influential midfielder Peter Leven who was withdrawn at half-time after feeling unwell.
One player who will be available is striker Justin Richards after he missed the midweek draw as he is on loan from the Brewers.
His return gives Chris Wilder a striking headache after James Constable scored on his return from suspension alongside Tom Craddock.
Oxford sit just four points behind their weekend opponents, with the Shrimpers currently occupying the final play-off place in npower League Two.