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 People: “I was too young, just 16 at the time.
“I went down to train for a week and really enjoyed it. I played for my team, Hamilton Accies, on the Saturday and Liverpool asked me back to play in a closed-door game.
“It was brilliant – Peter Crouch and Dirk Kuyt were playing. Everything about it was great. I played for the reserves in the first half and they switched me to the big team in the second half.
“I scored a goal … it just sat up for me at the edge of the box and I hit it into the top corner past Jerzy Dudek.
“But it wasn’t for me at the time. If I had gone to Liverpool I would have been stuck in the reserves and not playing much. Playing first-team football was my main aim – that was my dream.
“Some of my mates wound me up and said I should go, but I was happy with my decision. I was also settled at home and didn’t want to leave my mum and dad.
“I had just left school and it would have been hard to leave home. I thought the best thing for me was to get my head down and just keep on playing, and that’s worked out.
“I am delighted with the way things have gone. I played over 100 games for Hamilton and then I got this move. It couldn’t be better.
“Now I’m going to be competing against the likes of Steven Gerrard and Yossi Benayoun – two players I really look up to – so I know I made the right move.”