Their Championship clash against Hull City was a must-win, however Posh were beaten 3-0 by their fellow relegation rivals.
The defeat leaves them glued to the bottom of the table - eight points from safety and with a game in hand over 21st place Reading.
Peterborough will now host Premier League champions Manchester City in the FA Cup Fifth Round tonight.
The two sides have only ever met once previously - another cup tie in February 198 - where the visitors came out 1-0 winners at London Road Stadium.
Peterborough United will then face another tough test in Huddersfield Town in the Championship on Friday evening.
The Terriers currently sit third in the league and are vying for an automatic promotion spot.
Here are the best of today’s transfer rumours...
9. Blackburn Rovers ace unlikely to sign new deal
Blackburn Rovers boss Tony Mowbray has said it ‘doesn’t look like’ Ryan Nyambe will re-engage talks with the club as his contract nears an end. The defender joined Rovers’ academy aged 13. (The 72) | Getty Images