The forward wants to leave for a club where he can play more regularly in the coming year.
Reports have linked him to Brazilian giants Flamengo, as well as European teams.
Per the Daily Echo, the Saints are open to selling the Argentine youth international.
Martin said: "I think it's ongoing. I think there's definitely interest there from a club.
"I don't deal with that side of it. Phil (Parsons), Rasmus (Ankersen) and the ownership group deal with all of that and then I'm informed once it gets close or is done.
"Then, I'll speak to Carlos about it. He's trained brilliantly. He's here and whilst he's here, he'll be available for selection.
"If it's a good fit for the club in terms of the finances involved and a good fit for Carlos, then he will go with everyone's best wishes.
"If he doesn't, he'll be here and he'll be our player - so I'm fairly relaxed about it.”
