Ibrahimovic has been out since April, after sustaining a serious ACL knee injury.
The Swedish striker landed awkwardly during the Red Devils’ 2-1 win over Anderlecht in the Europa League.
Ibrahimovic underwent surgery and is now close to a return.
In an interview with MUTV, the 36-year-old praised Lukaku, who arrived at the club last summer.
“Yes, he’s doing fantastically well, but it’s no surprise. The only difference now is that he’s doing it at a big club, with all due respect for Everton and all the other clubs he played for.
“Now he’s doing it on the big scene where the pressure is totally different. I think when you’re playing for a top five club in the world the pressure is different compared to other clubs, with all due respect to them.
“And now he’s doing it on the big scene, he’s showing what he’s good at – scoring goals – he’s a powerful machine. And I think he’s doing exactly what he needs to do – scoring goals and using his power, and not doing things he’s less good at and things he doesn’t need to do.
“He’s around 10 goals I think, so that’s been a big help to the team and as long as he’s scoring the goals I have less pressure to come back fast and the help he gives the team is even better. Hopefully he can continue being on that track producing like he’s doing.”