Allardyce had to move midfielder Alou Diarra into a deeper role during the 1-0 defeat by Manchester United in the FA Cup fourth-round replay at Old Trafford.
The Hammers boss felt Diarra equipped himself well in the role, but Allardyce is aware he will have recruit experience for the second half of the league campaign.
West Ham have been linked with Blackburn defender Martin Olsson, who is thought to be the priority target for Allardyce.
"We will try and get some defenders in as quick as we can," the Hammers manager said.
"Alou Diarra did a fantastic job today top help with our defensive side - of players availability because we've only got Winston Reid, James Tomkins and Guy Demel who are experienced defenders."