Lukaku netted a late brace, as the Serie A club booked their place in the Europa League final, with a comprehensive 5-0 win over Shakhtar Donetsk on Monday.
The Belgium international would have been facing familiar faces, if United had not lost 2-1 to Sevilla in their own semi-final.
It meant United ended the campaign trophyless under Ole Gunnar Solskjaer. But Lukaku feels the Red Devils are well positioned for success next season.
“United tried their hardest. I think they had a really good season, I think Ole did a good job, the players did really well.
“[Mason] Greenwood is coming through, [Anthony] Martial, {Marcus] Rashford, I expected all of that – I’m really happy for them.
“They look really good for next season, I have no doubt,” Lukaku told BT Sport.