Cotterill was speaking after seeing his side rescue a dramatic late point at home to Derby as David Nugent cancelled out Steve Davies' first-half volley.
He said: "We do need to be stronger here (at Fratton Park). It's very difficult. We were at home and potentially we wanted to start at 4-4-2.
"We wanted to do that but we are a player missing. If we still had John Utaka (who was the latest player to exit when he joined Montpellier earlier in the week) we would have gone 4-4-2 from the kick-off. But we need someone to balance off that left-hand side for us. It has been a headache."
Portsmouth started with an on-loan backline, and Cotterill added: "When I went into the stand (to watch the second half) someone said `You need to get a back four, Steve`. Well that's great, but it would probably cost us about £3million if we wanted to get some good ones.
"Does anybody not think I want that? You give me the money and I'll spend it - 100%. But I'm working with what I have, and quite often we've had four loan players at the back. How ideal is that?"