While Martinez wants to keep the former Hamilton virtuoso at the DW Stadium for as long as possible, he admits he will not stand in his way when he feels ready to follow the likes of Antonio Valencia (Manchester United) and Victor Moses (Chelsea) in joining one of the world's elite outfits.
"That's the nature of the game," the Spaniard told the Wigan Evening Post. "I'm pleased to see him improving, enjoying his football, taking responsibility and putting in performances to get good results for Wigan Athletic.
"James McCarthy's got the potential to play anywhere in the world and whenever he's ready we'll never stop him.
"But James McCarthy is at a very good club now and we want top players to stay here for as long as we can.
"That's why I invested a lot of money when he was young. I think technically it is difficult to find a better player.
" At 22 to have the tactical awareness that he has and to be so consistent week in week out, James knows he needs another period of improvement.
"But from a technical point of view he can play in any team in the world and he will do one day.
"We just enjoy seeing him grow and seeing him enjoy his football and being important player for us and at international set-up."