The World Cup-winning centre back, who has three years left on his current deal at the Allianz Arena, is also being eyed up by Arsenal ahead of deadline day on August 9, while French side Paris Saint-Germain are believed to be monitoring the situation as it unfolds.
It became clear some time ago that Boateng would be allowed to leave Bavaria this summer if the right price was paid for his services, and Bayern Munich's magic number is believed to be in the region of €50m (£45m).
Manchester United have taken their first step in acquiring Boateng's signature this summer, according to Sport Bild's Bayern guru Christian Falk, by opening negotiation with the Bundesliga giants ahead of the new season.
Rival publication Kicker, meanwhile, have also thrown Arsenal and Paris Saint-Germain into the mix. Boateng has supposedly seen a move to the French capital fall through already, but Les Parisiens' manager Thomas Tuchel remains eager on signing his compatriot.
The 29-year-old defender was among a handful of names that Manchester United boss José Mourinho gave to executive vice-chairman Ed Woodward at the start of the transfer window, but talks have only just begun after deals for other targets failed to get off the ground.
"'If we don't make our team better it will be a difficult season for us," Mourinho said about the club's transfer business, quoted by the Daily Mail. "My CEO knows what I want for quite a long time, I know he tries to do the best for me and I still have a few days to wait to see what happens."
Bayern Munich's sporting director Hasan Salihamidžić has already attempted to play down the negotiations with United following questions from Bild in Germany, claiming: "You know very well that we are not talking about it."
The Bundesliga champions are supposedly keen on letting Boateng leave this summer as it would act as the catalyst to sign France international and World Cup star Benjamin Pavard, who plays his club football as a centre back.
The extent of Arsenal's interest in signing Boateng ahead of the new season is currently unknown. However, newly appointed chief scout Sven Mislintat will be keen on the move following his time with Borussia Dortmund.
Similarly, it is also unknown how far Ligue 1 champions PSG will go to land Boateng this summer, although the club have already seen one deal for the defender fall through during the current transfer window.