Bobby Charlton impressed by 'exciting' Sergio Aguero

Sir Bobby Charlton believes Manchester United are well placed to retain the Barclays Premier League title but expects an "exciting" battle with a Sergio Aguero-inspired Manchester City.

City threw down the challenge to the champions on Monday as record signing Aguero enjoyed a sensational debut at the Etihad Stadium.

The £38million summer buy came off the bench to score twice and set up another goal as City launched their campaign with a 4-0 thrashing of promoted Swansea.

Sir Alex Ferguson's side were less convincing as they began their quest for a record-extending 20th title with a 2-1 win at West Brom on Sunday, but United legend Charlton is confident enough.

Charlton, 73, said: "He is marvellous, Alex. I don't know how he does it.

"Every year he comes up with something different - change of coach, change of players - he is just fantastic.

"We are there again, ready for the 20th."

He added: "Yes, I saw City. I watch all the football.

"The new lad's played really well. He'll be a hero.

"He is a class act and Manchester City have the wherewithal to get all the best players.

"But we shall see - it is getting exciting."

One early worry for United has been the form of new goalkeeper David de Gea.

The Spaniard, signed from Aguero's former club Atletico Madrid in the summer, was criticised after conceding twice in the Community Shield earlier this month and was also at fault for West Brom's goal at the weekend.

The 20-year-old has a tough task to fill the void left by the retired Edwin van der Sar but Charlton is convinced he will come good.

Charlton said: "He is a great goalkeeper and we knew about that when he was coming.

"But you have got to remember he has arrived in a strange city, a strange country where they don't speak the same language and they are more passionate about football than anybody, even in Spain.

"But Alex will work his magic and the staff will work their magic, and he will be one of the great players by the end of the season, definitely."

Ferguson has also freshened up his side following the retirements of Gary Neville and Paul Scholes by bringing in Ashley Young and giving a chance to a number of youngsters.

Charlton believes Ferguson, who will this year celebrate 25 years in charge at Old Trafford, has made the correct calls again.

He said: "I am really impressed with them.

"I think Alex surprised a lot of people by fielding a team like he did initially but he is always right. I don't know why, but he always is."

:: Charlton was speaking in Salford at the launch of the Laureus 'Urban Stars' project, which aims to engage disenfranchised youngsters with society by encouraging them to play sport.