Scotland Yard confirmed the United supporter from Wales, who has not been named, will not be charged after the woman steward told police she did not want to pursue the matter.
The alleged incident during the game at The Valley on Saturday November 19 last year resulted in Charlton threatening to ban all Manchester United fans from The Valley.
The United fan was arrested at the match and held in custody for questioning before being released on police bail.
However a Scotland Yard spokesman said: "A 21-year-old man arrested at the game for allegedly sexually assaulting a female steward has been told he will face no further action after the alleged victim indicated to police she did not want to pursue the matter."
[There’s no news yet about whether the ludicrous claims made by Charlton’s chief exec Peter Varney of seats being throw about have also been withdrawn.]