It will be set after the events of the Manga.
It has been announced that a new Anime Movie based on the franchise of Prince of Tennis is in the works, the announcement came from the mouth of its creator, Takeshi Knomi, who is working as executive producer for this film.
The Movie will cover the events between Prince of Tennis and Prince of Tennis II Manga, covering some events that happened to the characters between the 3 months that passed.
Other details are still unknown.
Via: Anime News Network