O'Neill decided to hand Olympiakos keeper Carroll an international lifeline after Camp's withdrawal, ending a six-year absence from the side.
Carroll has insisted that he would welcome competition from Camp if he returned to fight for a place in the team.
The 35-year-old told Sky Sports News: "I liked the fight for number one. Me and Maik Taylor did it for a number of years and I think we liked the competition.
"I have been in two squads with Lee before and he is a quality keeper. He spoke to me and said he had to go home, because he has family things to see to, and said he was sorry to go.
"He is a good lad, is still young as a goalkeeper. I know what it is like, I was out for six years so I told him he can't leave it as long as I did, he has to come back as soon as possible and get more caps."