United, meanwhile, are 20 points behind their neighbours in seventh place. They are likely to miss out on European qualification altogether thanks to a disastrous campaign under David Moyes, who was recently fired just 10 months after being appointed successor to Sir Alex Ferguson.
But the club's all-time top goal scorer, who is now a director at Old Trafford, has told City the balance of power will swing back in United's favour next year.
"This year has been a tremendously interesting year," said Charlton, who played 758 times for the club.
"We have done our best, we have changed manager, and it has not worked. But next year I guarantee that we will be number one in Manchester."
Charlton confirmed that Moyes' successor, likely to be Louis van Gaal, will have money to spend.
"We will have to buy a couple of players, which will happen," added Charlton, who was speaking at the Manchester United player of the year awards.
"I am looking forward a lot to next year because Manchester United is not renowned for being second.
"We like to be first and we will be first. We have the most fantastic organisation and that organisation when it works is unstoppable."
Van Gaal's appointment will not be confirmed until after Ryan Giggs' final game of his interim spell as player-manager on Sunday at Southampton.
Giggs could play on for another year, join the new manager's backroom staff or manage at another club.
The Welshman picked up the United lifetime achievement award at Thursday night's ceremony at Old Trafford - an honour usually reserved in sport for those coming towards the end of their careers.
But Giggs insists he has not yet made his mind up yet.
"I have not decided," the 40-year-old said.
"I am too busy trying to prepare a team for Southampton and that is my priority at the moment.
"When the season ends I will go away and think about what I want to do next.
"I said five or six years ago that if my career ended tomorrow I would be happy so every year is a bonus.
"I still enjoy training and playing but I have really enjoyed the last couple of weeks so it has been a good experience to take me on to the next chapter of my life."
Just like Charlton, Giggs is sure United will perform much better next season.
"It's been a disappointing season but if you are a proper club, which we are, you always bounce back," said Giggs, who made his debut for United in 1991.
"In football you have setbacks. In my first full season we lost out to Leeds in the league and I was sat in the dressing room as an 18 year-old watching grown men cry.
"We came back the next year and won the league for the first time in 26 years and there is not a doubt in my mind that we will be back next year, we will be challenging and that is what proper clubs do - they have setbacks and come back stronger."