The 19-year-old turned down a £1million move to Liverpool while he still was at Hamilton three years ago.
McCarthy joined Wigan in a £1.2million deal from the Scottish side in the summer.
He told the Sunday Mirror: “I have always been a big admirer of James and I followed his career for a long time.
“When a youngster gets to play at such a young age it makes you sit up and take notice.
“That meant I was delighted when he made that rather strange decision not to go to a top, top club like Liverpool.
“I think that decision is being proved right now.”
