Left-backs Tom Kennedy and Grant Basey are both sidelined while right-back Mark Little also missed the 1-1 draw at Huddersfield on Saturday as Ferguson has seen his side win just once in their last five games.
He said: "We were able to field a settled back four when we were regularly keeping clean sheets, but since then we've had to shuffle things around a bit with injuries.
"The injuries have been a pain and something we could have done without, but other clubs are in the same boat. It is irritating, but we can't make excuses. You just have to get on with it.
"Hopefully we can get back into a position where, all being well, we can select the same lads on a regular basis again.
"We have let in far too many goals lately - especially the two against Bristol Rovers and the three against Bournemouth - and we need to get back to keeping clean sheets as a team."
Source: PA
Source: PA