HOUSTON -- Kevin De Bruyne believes that Romelu Lukaku is one of the best strikers in the world after his £75 million move to Manchester United this summer.

The Belgium international teammates are now on opposite sides of the city and Lukaku has already made an impact, scoring the opening goal in United's 2-0 victory over Manchester City in the International Champions Cup on Thursday.

Some fans and pundits have questioned whether Lukaku will be able justify his expensive price tag, but De Bruyne has no doubt that the former Everton forward will be a success at Old Trafford.

"I think he will do very well. Everyone knows what his qualities are and he will do what he has to do," De Bruyne told reporters after the first ever Manchester derby outside England.

"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.

"You just have to do your job and I think he will score 20-25 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.

Kevin De Bruyne thinks Romelu Lukaku will score 20-25 goals in a season with Man United. Kevin C. Cox/Getty Images

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

United are not the only club to spend heavily this summer with City already investing £120m on midfielder Bernardo Silva, goalkeeper Ederson and defender Kyle Walker with more set to arrive.

Silva will provide more competition for De Bruyne as will 17-year-old academy player Phil Foden, who impressed manager Pep Guardiola in the defeat to United.

"Since I've been here we've seen a lot of change. We bought a lot of young players, we have a little project coming on," added De Bruyne, who joined City from German club Wolfsburg in 2015.

"I now feel like I'm one of the older ones and I'm only 26 so it's nice to see that there's so much young talent around now.

"[Foden] is very good. He did really well [against United] and he has a big future. He can be one of the big players but he's only 17.

"I haven't seen [Bernardo] yet. I think he's played most seasons for Monaco on the right -- but he can play in the middle. We play a lot of games and it's always necessary to have competition.

"We have Raheem [Sterling], Leroy [Sane], Patrick [Roberts] -- a lot of guys who can play wide too. I'm ready to do what I can."

City's clash with United was their first of preseason, and De Bruyne said not too much should be taken from the result.

Guardiola's side face Real Madrid in Los Angeles on Wednesday and Tottenham in Nashville on Saturday and he expects their performances to quickly improve.

"It was only the first game. We tried to play a good game but in the end maybe United were a little bit sharper than us. The way we played was great, but it was the first game," he said. "We need to go into these games fully. because we need to prepare.

"This year we want to win trophies -- and that's what we need to do as a club like City -- but we are not the only one with that aspiration. There are six or seven others as well."