Martinez worked with Lukaku at Everton.
“He is still a very young player but he has coped easily with the expectations and whatever Man United put on him.
“I can see he is really enjoying being in a team where there is very little margin for error.
“He is one of those players that sets himself little targets and you can see he's on track.
“For us, it's important that we see that continue over a ten-month competition."