Romelu Lukaku has matured at Manchester United - Roberto Martinez

Moving to Manchester United has made "a big difference" to striker Romelu Lukaku, Belgium coach Roberto Martinez has told talkSPORT.

Martinez, who worked with Lukaku at Everton, said the striker had matured since moving to Old Trafford, where he has scored seven goals in as many matches.

Lukaku moved to Manchester in a £75 million switch from Everton, and Martinez said he had always expected him to shine at United.

"I have seen a big difference in terms of his maturity when he comes to international camps," he said.

"From the young player I signed, it is the same goal scorer but with an incredible maturity. That is great to see, and he still has many, many years to develop.

"Everyone who plays with him or works with him realises very quickly that he has an elite brain.

"When he went to Manchester United, he was solely focused on starting well and making a big impact -- and that is what he has done."

Martinez said that although Lukaku was still a young player, saying people "sometimes forget he is only 24," he "wants to carry on developing" and would be able to do so under United boss Jose Mourinho.

He added: "He is with a manager with whom he will keep learning different aspects at club level."