The Ireland midfielder has been heavily linked with Tottenham over recent months, with McCarthy reportedly unhappy that he has yet to be offered a new contract. In recent days former Wigan man has again been linked with a move away from the club, this time to Manchester City.
Following Fabian Delph's last-minute decision to stay at Aston Villa City boss Manuel Pellegrini is on the lookout for another bench-warmer to fill his home-grown quota in the Champions League next season.
When quizzed about the latest reports Martinez was quick to play them down, insisting McCarthy was part of his plans at Goodison Park:
"He’s not for sale.
"My responsibility is to try to keep bringing competition into the squad. I think what we have got now is a very strong competition for places and we don't want to lose that.
"We are not in a situation at this football club that we have to sell to balance the books. What we want is to be successful and create a winning team.
"James McCarthy has been a top performer in the last few seasons. At the age of 24, to be over 300 games shows the know-how he brings, together with young legs and good energy.
"He is a vital part of our squad.
"It's important that we keep improving, keep getting stronger and that is the only focus we have - not losing assets."
Despite Everton once again being relative paupers in the Premier League transfer market, the new TV deal - which began last year - has steadied the financial ship at Goodison Park.
Unlike the during the David Moyes era the club does not need to sell a key player to balance the books and with three years still left on McCarthy's deal they can reject any advances from a position of strength.
However, City have just spent £49m on a relatively unproven 20-year-old so if they want McCarthy they will get him - as long as they pay.
Losing the midfielder would be an undoubted blow as his lung-busting efforts in the centre of midfield have become a key asset in Martinez's side.
But if City are prepared to pay silly money - and I'm talking upwards of £30m - then that would soften the blow considerably.
Whether they are prepared to do so remains to be seen so Everton would do well to sort out McCarthy's contract situation now or risk another transfer battle next summer, only from a much weaker negotiating position.