Joe Walsh and Scott Golbourne are likely to miss the rest of the season through injury, throwing Robbie Neilson's transfer plans out the window, but there is little chance of a Dean Lewington return.
Both defenders require operations, and with Golbourne's loan deal now up, he will return to parent club Bristol City, but Neilson said exiled Lewington is unlikely to make a return.
It means rather than recruiting in the attacking third, as had been Dons boss Neilson's plan since the transfer window opened, he is now seeking cover at the back.
"The two of them will need operations and will be out for an extended period, probably the end of the season," Neilson confirmed after the 0-0 draw with AFC Wimbledon on Saturday. "It's a big disappointment for us so we will have to recruit in those areas now.
"Things have changed dramatically now. We have had a lot of boys out injured, and it has been difficult to get a run of games with the same players. The two are big players for us, but they're out now, so we have to move on."
Neilson had previously hinted at signing Golbourne on a permanent deal this month, but with the left back now set for a spell on the sidelines, the manager will look elsewhere.
He said: "We will reassess things in the summer. He's going for an operation so will go back to Bristol. We will see how he is in the summer, see how his fitness is and go from there."
Neilson though denied there was a chance for Dean Lewington to return to the fold - the former skipper, now training with Charlton, will be overlooked as the manager seeks out another left back.
When asked about a second chance for Lewington, Neilson said: "We're looking to recruit in that area, We'e got a number one target so we're trying to push that one."
Meanwhile, Neilson hopes to have Ike Ugbo back for the trip to Northampton. The young Chelsea striker missed out on the home game against AFC as part of his loan deal, the manager explained. "We had an agreement with Chelsea - he was supposed to come after this game because he was due to play for hte U21s tomorrow but they let us take him early.
"We were worried someone else would take him before we could get him. He'll be back with us in the week."