The incident occurred after Thomas missed a par putt during the Sentry Tournament of Champions’ third round in Hawaii.
“I’m an adult. I’m a grown man. There’s absolutely no reason for me to say anything like that.
“It’s terrible. I’m extremely embarrassed. It’s not the kind of person that I am … But unfortunately I did it and I have to own up to it and I’m very apologetic.
“I deeply apologize to everybody and anybody who I offended and I’ll be better because of it,” added Thomas.
“As he expressed after his round, we agree that Justin’s comment was unacceptable,” the PGA Tour said in a statement according to the AFP news agency, which added Thomas is likely to be fined for conduct “unbecoming of a professional.”
Going into Sunday’s final round Thomas is tied for fifth place, four shots behind co-leaders Harris English and Ryan Palmer.