It's been a turbulent three years for the Belgium international - on loan from Chelsea at the Serie A club - having initially quit England for Italy in 2019 when he left Manchester United.
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After two stellar campaigns with Inter, where he scored 64 goals in 95 games, he was re-signed by Chelsea, where he first played as a teenager, in a £97.5million deal.
His return, though, did not go smoothly and, despite a decent start, injuries and manager Thomas Tuchel's decision to change his tactics saw him fall out of favour.
Lukaku then conducted an infamous interview with Sky Italia, where he revealed his unhappiness at Stamford Bridge after the alterations, which did not suit his style of play.
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He ended last season with 15 goals in 44 appearances and has now returned to Inter on loan.
Asked about his struggles at Chelsea compared to his form for Belgium, where he was able to score four goals in four games over the same period, national boss Martinez insisted his own talent can sometimes see him misused.
He told talkSPORT: "You rely a lot on how you are used. It's not the same using your qualities when you are a possession team, or you play on the counter attack.
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"Rom is a player who can play in many different profiles. He's a no.9, he can run in behind, and probably he's a victim, sometimes, of his versatility and the way he is used at club level.
"But he's a very settled player in the national team, he's got a huge role, and a huge responsibility for us.
"We saw a big difference when he went to Serie A, when he went to Inter Milan the first time round. I think he developed a degree of maturity that I didn't see with him - and I worked with him when he was a young player at Everton at the age of 19.
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"He's always been a sensational goalscorer and then you can pick out whatever you want, you can try and look at the things he hasn't got but if you have got an exceptional goalscorer with a real degree of maturity, it's always a very important player to have, especially in our national team."
Legendary Arsenal and France goalscorer Thierry Henry is one of Lukaku's coaches at international level where he has scored a record 68 goals for his nation.
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And Martinez believes his energy and experience make him the perfect man for the 29-year-old to seek advice from when the going gets tough.
He added: "Thierry, first of all, has got this passion for football. I think when you hear him talking about the game, it's his life, it's what he feels and it's so contagious.
"He's become a coach that can use his own experience in a very good way and you would love to work with him.
"As a striker all you want is to get that little bit of an insight into the way that he performed as a striker. It's the best substance you can have as a coach.
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"When it came to Belgium, I had never managed internationally and I didn't know what it meant to go into a major tournament.
"With Thierry, it's not just that he's been at a major tournament, it's that he's won the World Cup, he's won the Euros and he can be a good sounding board for any player."
After a spell on the sidelines this season, Lukaku returned with a goal in the Champions League this week as Inter beat Viktoria Plzen 4-0.
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And Martinez is hopeful his team's key forward will be fit to star at the 2022 World Cup in Qatar.
"It was great for him yesterday to come on," he said. "It's the first soft tissue injury that he has had so it was a two month period where it was difficult, but for him to come on and score his goal, first game since August, it's really good return and he's a really important player to be match fit for us."