Manchester City midfielder Kevin De Bruyne has backed new Manchester United striker Romelu Lukaku to prove that he is worth the hefty transfer fee the club parted with to secure his services.

United spent an initial fee of £75m to bring Lukaku to Old Trafford from Everton, although that could rise as high as a world-record £90m depending on bonuses.

Lukaku scored his second goal for the club in a 2-0 pre-season win over De Bruyne's Man City on Friday, and the Belgian believes that his compatriot will be a hit for Jose Mourinho's side.

"I think he will do very well. Everyone knows what his qualities are and he will do what he has to do. There's a lot said about these big transfers, people mock him and other players on social media. You know it's there but you just can't care about that," he told reporters.

"You just have to do your job and I think he will score 20 to 25 goals for United a season and that will speak for itself. If you see his ratio of goals, it's incredible. He's one of the best in the world and what is he, 24? You can say that about him at that age.

"Obviously he has his way of playing. Don't compare him to a [Lionel] Messi dribbling past players. He's a big physical guy and can be awesome."

Lukaku scored 25 Premier League goals for Everton last season.