MK Dons could get relegated even if they win on Tuesday night after a pitiful 4-0 defeat to Southend on Saturday.
Theo Robinson scored twice in the first half, and completed his hat-trick after Stephen McLaughlin's second-half header to complete the rout.
With the gap now six points to safety, Dons could be officially confirmed to be playing League 2 football when they travel to Bradford City on Tuesday night.
MK Dons made two changes to the side which got beaten by Doncaster Rovers a week earlier. After Peter Pawlett picked up a knock in training, Ouss Cisse returned to the side in the centre of midfield as Dan Micciche reverted to a 4-4-2 formation. Scott Golbourne was the other player to miss out, replaced by Marcus Tavernier.
Wieger Sietsma wouldn't have been too pleased by his own perfomance against Doncaster, and he was at fault again for Southend's opener. After a drab opening 20 minutes, Dru Yearwood battled through the midfield to get a shot away. While the Dutchman got a hand to it, but palmed it directly into the path of Theo Robinson who routinely tapped in the opener.
Heading into the game, Dons knew they would need a point at the very least from the afternoon, but their task was made even harder eight minutes later when Robinson doubled his tally, exchanging a quick one-two with Michael Timlin before brilliantly lofting the ball over Siestma's head and into the top corner.
Dons barely threatened in the opening half hour, though the battle between Chuks Aneke and John White was proving to be a tough and physical one. But the Dons striker should have done better when he managed to get a yard ahead of his marker, only to fire wide from eight yards out.
Sietsma tried to make up for his earlier errors by making a fine double-save to deny Southend a 3-0 half time lead, first keeping out Marc-Antoine Fortune one-on-one before tipping over Stephen McLaughlin's effort from the edge of the box as the home side sought to put the game to bed before the break.
It was much the same story in the second half. Withdrawing the anonymous Marcus Tavernier at the interval did little to change things as Robbie Muirhead struggled to make headway, while at the other end, Dons were picking the ball out the net again on 63 minutes when McLaughlin flicked on Michael Kightly's free kick from the Southend left to put the hosts 3-0 to the good.
Things went from bad to worse 13 minutes later when Robinson completed his hat-trick, heading in from close range as Dons failed to clear a routine corner.
Referee: Gavin Ward
Attendance: 7,546 (390)
Southend United: Oxley, Ferdinand (Kyprianou 70), Kightly (Harrison 70), Timlin, Fortune, McLaughlin, Yearwood, Demetriou, Robinson (McGlashan 80), Bwomono, White
Subs not used: Bishop, Wordsworth, Cox, Ladapo
MK Dons: Sietsma, Williams, Wootton, Ward, Lewington, Upson (Agard 65), Cisse, Brittain, Tavernier(Muirhead 46), Ugbo (Thomas-Asante 74), Aneke
Subs not used: Jones, Reo-Coker, Golbourne, Ebanks-Landell
Booked: Tavernier, Aneke, Yearwood, Timlin