The Rovers squad has been hit by an outbreak of the virus, with three players and a member of the club's coaching staff struck down.
Their depleted troops came unstuck at Chelsea on Saturday, as they were hammered 5-0, and Sam Allardyce will be keen to avoid a similar showing in midweek.
Peterborough will fancy their chances of causing an upset, having made impressive progress en route to round four.
They have already seen off Wycombe, Ipswich and Newcastle, conceding just one goal along the way.
Darren Ferguson will now be eyeing a Premier League scalp, while he will also be looking for his side to build on a morale-boosting 3-0 victory over Scunthorpe in the Championship over the weekend.
Shuffle packAllardyce must again turn to his second string to help plug the gaps created by those struck down with swine flu.
Chris Samba and David Dunn, who both missed Saturday's defeat at Chelsea, are believed to have been struck down with the virus, along with an unnamed third player.
Pascal Chimbonda (calf) and Vince Grella (thigh) will miss out through injury but Allardyce is hopeful the pair will be available for the weekend's trip to Manchester United.
Franco Di Santo can be picked again having been ineligible to play against his parent club at the weekend, but as he has done in previous rounds, Allardyce is likely to rest a number of regular first-team players.
Duo doubtfulFerguson could be without Craig Mackail-Smith and Gabriel Zakuani for the trip to Ewood Park.
Striker Mackail-Smith scored his first goal in four games against Scunthorpe at the weekend but came off late on and is rated as a doubt while Zakuani is struggling with a hamstring problem.
On-loan Birmingham defender Krystian Pearce could come into the side but both of Ferguson's new signings will have to wait to make their debuts.
Ryan Bennett and Scott Griffiths were left on the bench on Saturday and are ineligible after featuring in the competition for Grimsby and Dagenham respectively.
Tottenham midfielder Danny Rose is also cup-tied while Paul Coutts (foot) and Tom Williams (ankle) remain sidelined.