Moyes insists there will always be a place for the workaholic midfielder, 31, as long as he is in charge at the club.
Moyes said: "Leon has got better with time.
"He's become an essential midfield player. He was always the one with the most football intelligence - you'd explain something to him and he'd know exactly what was wanted.
"I don't think he'll ever get the proper credit but as long as I'm here he will be here if he wants to be.