Lukaku joined Manchester United from Everton this summer for an initial £75m and he has made a blistering start to his Old Trafford career with four goals in as many games.
The Belgian also scored a crucial goal for his country last night to help them beat Greece and qualify for next year’s World Cup.
As the 24-year-old arrived at United, Rooney departed to replace him at Goodison Park.
And the former United captain believes Lukaku is the ideal striker for Jose Mourinho.
Rooney told talkSPORT: “For that United side, he is the perfect player.
“He is powerful, quick and strong and he scores goals, so certainly will improve that team.”
Another former United striker Ruud van Nistelrooy believes Lukaku will beat his scoring records.
Asked whether Lukaku can surpass his records, the Dutchman told Full Time Devils: “Absolutely. Yeah. I had my time.
“I tried to make the most of my time as a player, but [my] time’s gone, behind me.
“I’ve done what I could and now I hope that other players will go on and do better.”