Craig Alcock and Davide Petrucci come back into the reckoning for Peterborough ahead of the visit of Birmingham.
Defender Alcock came through a 90-minute run-out for the development squad this week having struggled with a knee problem recently.
On-loan Manchester United midfielder Petrucci missed the 5-1 win over Millwall in midweek due to a hamstring injury.
Posh boss Darren Ferguson had probably hoped to name an unchanged team following Tuesday night's performance at The Den, but winger George Boyd moved to Hull on loan on Thursday.
Teenage left-back Kgosi Ntlhe made his long-awaited comeback from injury in the development squad.
South African Ntlhe, sidelined since suffering a broken ankle against Sheffield Wednesday on November 3, played 45 minutes of a friendly against Stevenage on Wednesday afternoon.
He will play for the reserves again next week with a view to being back in first-team contention for the trip to Blackburn on March 2.
Lee Clark is waiting on the fitness of three players ahead of the crunch clash.
Callum Reilly and Paul Robinson are both struggling with ankle injuries, while striker Marlon King is a doubt with a knee injury.
Reilly and King had returned to the team for Tuesday night's goalless draw with Sheffield Wednesday but are facing a race to be fit for the pivotal fixture.
The Blues are four points above the drop zone after losing just one of their last seven fixtures
Midfielders Keith Fahey and Darren Ambrose are both back in training but the game is likely to come too soon following lengthy periods out of first-team contention.
Youth team attacker Koby Arthur will travel with the squad for the fixture and could be named on the bench.