O'Neill said: "I was perfectly happy with the money we received for Cahill. I was asked if I regretted it and said I really don't think you can see that far into the future.
"The injury was very unfortunate for Curtis (Davies), but that's why we took on another centre-half (Zat Knight). That was primarily because I never thought Martin would play that many games.
"He's played a full season which is remarkable, and we also had Olof Mellberg. I wasn't pushing Gary out the door, but I understand him wanting to play, especially as he was down the pecking order."