He said: "No disrespect to the players we brought in, but we couldn't really get what we wanted on the first round in the summer transfer window. We ended in the second or third area.
"I was looking for more Premiership experience. When I lost the opportunity to get those players, it then became hugely difficult.
"I saw that for the first time against Liverpool last week. I said to myself: 'We are short defensively.' Too many of our players at the moment are performing inconsistently."