Martinez has already spoken so highly of McCarthy, it is hard to imagine he will not leave at some point, with mounting speculation that he is being courted by the likes of Arsenal, Everton and Liverpool.
The crucial factor is if it will be at a time of Wigan's choosing.
Martinez said: "I always feel it is not about losing players, it is about how you are going to replace them. It has to be at the right time for the club. And also the right price.
"And we need to create a culture where we can keep our assets for a little bit longer."
Martinez is determined to resist any advances but, as he prepares to hand Angelo Henriquez a first start in tonight's FA Cup third-round replay at Bournemouth, he feels Wigan are a big enough draw on their own.
"I do see a change," Martinez said. "It is something that we had to do in the past. We needed to embrace it.
"The players were coming into a new league and they knew they could develop and move on. We had the benefit of getting outstanding talent.
"I don't think we are in that situation now. It was important we changed it.
"The players need to know what it means to represent Wigan."