The Red Devils legend "guarantees" that his old side will bounce back from their disastrous 2013-14 to regain their status as the top club in the city after "a couple" of buys
After a difficult year in which United were twice thrashed by Manuel Pellegrini's side, their rivals are now one win away from securing the Premier League title.
David Moyes was sacked in April as a result of the reigning champions' struggles, with the chance to leapfrog Tottenham into sixth place the most to which they can look forward on the final day, but Charlton is confident that they will be able to turn their fortunes around swiftly.
The club's record goalscorer told reporters: "This year has been a tremendously interesting year.
"We have done our best. We have changed manager and it has not worked but next year I guarentee that we will be No.1 in Manchester.
"We will have to buy a couple of players, which will happen. 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."