Scott Wootton struck in the 2-1 defeat, while Davide Petrucci also featured.
Ferguson told the Peterborough Evening Telegraph: "Davide was trying too hard to get involved in the first half and was dropping back too deep as a result. He was better when we moved him back and he got on the ball a bit more, but it’s obvious he needs games.
"We knew Scott was a very good defender so his performance didn’t surprise me. He played very well and I thought he had won us a point with his goal."