Barkley's displays for the Toffees in the Premier League this season earned him a spot in England's World Cup squad, but Martinez insists that seeing the midfielder's stock rise does not mean that his departure is a possibility in the transfer window.
"I would not sell even if we got a huge bid. It would be wrong for him," the Spaniard told reporters. "I always feel as manager you develop a relationship with players and you're always honest with that.
"Ross is a phenomenal talent, probably the best English talent I have ever seen, but he is not the finished article yet and you need to be very careful.
"It's our duty to protect him and I know Everton is the perfect place for him for the next 12 months."