Martinez revealed one of the reasons for targeting Lukaku was the 20-year-old's familiarity to English football and the Premier League.
"It was a perfect fit for what we needed and he is not going to need any settling in period," Martinez said.
"Clearly, he knows the league inside-out and he is not going to need any time to settle into the squad because he knows Kevin Mirallas really well from the international setup.
"I just see him as someone who can come in straight away and hit the ground running - and you don't get many players like that.
"As you can imagine, there were many clubs wanting Romelu but we are pleased that we managed to give him a challenge that he is looking forward to."
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