The incident occurred after Thomas lost a putt pair during the third round of the Sentry Tournament of Champions in Hawaii.
“I’m an adult. I’m an adult man. There is absolutely no reason for me to say something like that.
“It is terrible. I am extremely ashamed. It is not the type of person I am … But unfortunately I did it and I have to confess it and I am very sorry.
“I sincerely apologize to everyone and anyone I offended and I will be better off because of that,” added Thomas.
“As he expressed after his round, we agree that Justin’s comment was unacceptable,” said the PGA Tour in a statement according to the AFP news agency, which added that Thomas will likely be fined for “improper for a professional” conduct.
Going into Sunday’s final round, Thomas is tied for fifth place, four shots behind co-leaders Harris English and Ryan Palmer.