Lukaku scored a brace against Shakhtar Donetsk in a 5-0 win to send Inter Milan through to the Europa League final.
Speaking on BT Sport, he said: "United tried their hardest. I think they had a really good season. I think Ole did a good job.
"The players I think they did really well. Greenwood's coming through, Martial and Rashford, I expected all of that, so I'm really happy for them and they look really good for next season I have no doubt."