The Red Devils were beaten to the Portugal international's signature last summer with Jose Mourinho yet to be installed as their new manager.
But things haven't worked out for the talented midfielder at the Allianz Arena.
The 19-year-old only started six Bundesliga games, failing to score or provide an assist in 25 appearances in all competitions, and managing 90 minutes just once.
And German publication Bild claim the Bundesliga giants will sell him if an offer of £30.5m is received.
Bayern paid £28m to bring him from Benfica but could pay up to £60m depending on how successful he is for club and country.
Bayern Munich are ready to cash in on Renato Sanches Manchester United summer transfer targets Sun, June 4, 2017
Express Sport takes a look at who could be on Manchester United's shopping list this summer
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But they want to avoid his fee rising and are ready to offload him after failing to be convinced by his displays in his debut season.
And Bild claim United, along with Inter Milan, Juventus, Monaco and Marseille, are all showing interest in him.
Mourinho could reignite his interest after revealing previously that he was disappointed to to have signed the teenager.
"I arrived late," Mourinho said in April. "I signed in May, we started talking a week before, but completely out of the process. If I had arrived earlier, I'd fight for him.
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Jose Mourinho is keen to splash the cash this summer
"Manchester United watched Renato many times and maybe I did it even more. In so much time at home, I watched many Benfica and Portuguese league games, I got to know the boy better with time.
"He's in a a big club, in a league where he'll certainly be the champion. The club have players of very high level which belong to the structure, a little like Benfica."
The report suggests United could also be in the hunt for Douglas Costa with his days appearing to be numbered in Germany.
Bayern will consider letting Costa leave too – but only if their £35m valuation is met.