The Republic of Ireland midfielder, who looks set to miss Wednesday's visit of Hull City with a persistent hamstring injury, has impressed following his 2013 switch to Goodison Park from Wigan Athletic.
And Martinez is determined to ensure the midfielder's future is with Everton, who shelled out £13 million to secure his services.
"We rate him very, very highly, otherwise you will never have seen the sort of investment we put in him 16 months ago," the Spanish manager said.
"I'm delighted with his form. He can grow and get better. He's got a long-term contract. I see the interest and the potential interest, and it's a compliment.
"But James is a player we look forward to see in the Everton top for a long time."
Despite the anticipated absence of McCarthy, Everton are strong favourites to see off a Hull side who have lost four on the bounce and not won in six Premier League games.
However, Martinez feels the KC Stadium outfit are in a false position and expects a tough challenge.
He added: "This Hull team have kept that competitiveness, bringing in some high-quality players. Their results are misleading."
Everton sit 10th in the table following Sunday's 2-1 loss to Totttenham, having won just once in their last four league matches.
