Watford's Michael Kightly and Lloyd Doyley will be assessed ahead of the clash.
On-loan winger Kightly was forced off with a hamstring injury in last Wednesday's 2-0 defeat at Leicester and duly missed Saturday's 3-2 loss at Hull and he now faces a race against time to be fit for this weekend.
Doyley, meanwhile, has picked up a thigh problem and also faces a late fitness test.
Manager Sean Dyche will be hoping Doyley makes it against Posh with fellow defender Martin Taylor already sidelined with a collarbone injury which has ruled him out of the last two games. However, new loan signing Nyron Nosworthy is available after joining the club from Sunderland until January.
One player definitely available and hoping to make his Hornets debut is striker Craig Beattie, who sealed a loan move from Swansea at the start of this week.
Lee Tomlin's suspension means Peterborough boss Darren Ferguson will be forced into at least one change.
Tomlin was sent off for the second time in his Posh career after 37 minutes of the 3-2 home defeat to Leeds last weekend after hacking down visiting striker Andy Keogh and he begins a three-match ban.
Tomlin's absence could open the door for Paul Taylor to return to the side while David Ball is another option for Ferguson, who has named the same starting XI for the past three matches.
Craig Alcock was forced off at half-time against Leeds due to a leg injury but the full-back should be fit for Saturday.