Despite being just 25 years of age, the Red Devils star is already preparing to call time on a career with his country.
As things stands, he intends to grace Euro 2020 and then walk away.
That means he will play no part for the Belgium in their 2022 World Cup campaign, when football’s showpiece event heads to Qatar.
Lukaku told Business Insider: “After the Euros, I think I'll stop.”
A man who currently has 75 caps and 40 international goals to his name has already graced two World Cup finals.
He has helped Belgium to become serious challengers for the grandest of prizes, with Roberto Martinez’s side reaching the last four and finishing third at Russia 2018.
“Every big tournament for us as a country has to be getting into the semi-finals, and then you go from there,” Lukaku added.
“You will go to win the whole thing, but you don't go for less than the semi-finals.”
While Lukaku has helped to push a golden generation of talent into contention for top awards, he feels that the time is approaching to let the next batch of potential come through.
He said: “I'm 25, I'm like, I'm not even in my prime yet.
“So I still see them as competition right now because they try to take my spot and I don't want to give it up to them. So like another two years, and then they can have it.”
If Lukaku does head into international retirement in 2020, he would then be freed to focus his full attention on events at Manchester United.
The five-year contract he penned with the Red Devils upon his arrival in a £75 million ($95m) deal is set to take him through to 2022 – with that agreement including the option for a 12-month extension.