Casey said in an interview with The Sunday Times of London in November that he learned to 'properly hate' the Americans during the Ryder Cup. He also said U.S. fans can be 'bloody annoying,' and the vast majority of Americans don't know what's going on in the world.
Casey later said he didn't need to apologize, only explain what he meant by his remarks.
'The players I spoke to about everything that had gone on showed understanding. But it was all the people to whom I couldn't give an explanation that concerned me and prompted me to get professional help,' Casey said in Tuesday's Daily Telegraph.
Casey made his PGA Tour debut at the Sony Open last month in Honolulu, where he missed the cut at 9 over par and got a cool reception from some of his peers. He withdrew from his next two tournaments.
'This whole mess is entirely of my own making, but as everyone will understand, I have to be able to put it behind me at some point,' Casey said.
He is playing in the Nissan Open in Los Angeles this week, then the Match Play Championship outside San Diego.
Scrutiny increased when, after the story appeared in The Sunday Times, the Daily Mirror wrote a headline with Casey saying, 'Stupid Americans: I Hate Them.' Casey was never quoted in the Times as calling Americans stupid.
'I don't think anyone has been more affected and upset than I have,' Casey said. 'The hurt I've caused will live with me as a huge source of regret for the rest of my life.'
Casey played at Arizona State, has an American girlfriend and swing coach and still lives in Scottsdale, Ariz.
'I've always cared deeply about the country and will continue to do so,' he said.