Lukaku scored seven goals in his first seven games in the Premier League for United, following his summer move from Everton, but hasn't found the back of the net since a 4-0 win over Crystal Palace on Sept. 30.

"I think Romelu is an out-and-out goal-scorer and his numbers reflect that," said Martinez in an interview with ESPN FC. "Only elite footballers get anywhere near his return in terms of goals so far in the Premier League. He'll tell you he's obsessed with the game, he wants to become better and work hard to fulfill the enormous potential that he has."

Martinez helped develop the striker while both men were at Everton and says the progress Lukaku has made in his career leaves him "happy" and "proud," pointing out that the player's age means he can still improve.

"He needs to be given a path and I think that path now is the move he had from Chelsea to West Brom, from West Brom to Everton and then after playing in Europe for Everton in an important role, going into Manchester United in a team that you're always expected to win; I think it's been a really interesting stage or path for Romelu," Martinez said. "Through that path you're going to have good moments, bad moments, but I think we're all aware that the enormous talent that he has in front of goal will allow him to go through any bad spell."

Manchester United manager Jose Mourinho has urged fans to back Lukaku and stressed that he should be judged on more than goals.

For Belgium, Lukaku has not had any problem scoring and netted 11 in eight appearances -- at a rate of one every 57 minutes -- in World Cup qualifying, helping the Red Devils top Group H in UEFA qualifying to secure their place at Russia 2018.

Lukaku also benefits from working with Thierry Henry, a Belgium's assistant coach, and Martinez spoke to the experience the former French international can offer a team of which much is expected.

"Thierry's been through what these players are going through," said Martinez. "I think that's very important in the group. His attention to detail is second to none for someone who has been one of the best footballers of his time; to be able to pass on those experiences to our players is essential and, as you can imagine for strikers in the group, it's a really good opportunity to share experience and to give them knowledge that is very beneficial. His role has been fantastic and we need to use his experience going into the World Cup."

Martinez added that he believes Henry can make the step from assistant to head coach in the future.

"Absolutely, without a doubt. I think Thierry is one of those people who'll do whatever he wants to do. He's capable of doing that. It's only natural that further down in his career, whenever he feels that it is right and it's the right environment, he'll make that step up, without a doubt."

On Friday, Belgium face Mexico in a Brussels friendly, then take on Japan next Tuesday.