Sanches, 20, was intensely linked with a move to Old Trafford in 2016 with Jose Mourinho critical of the club's failure to sign the midfielder from Benfica. The former Chelsea manager arrived at the club to replace Louis van Gaal in May 2016, but his appointment came three weeks after Bayern had wrapped up a deal for the Portugal international.
"I arrived [at Manchester United] late," Mourinho later recalled. "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."
Sanches, regarded as perhaps the brightest young talents in Europe when Bayern and United were vying for his signature, endured a difficult first season in Germany however, making just 25 appearances in all competitions with the midfielder later admitting he had "expected more" from his first season playing under Carlo Ancelotti.
With the arrivals of Corentin Tolisso from Lyon and Sebastian Rudy from Hoffenheim, Bayern now admit Sanches will be best served leaving on a temporary basis in the coming weeks.
"We will decide when we have completed our shopping whether to keep him here or loan him out for a year," Bayern director general Karl-Heinz Rummenigge said. "He really needs playing minutes after the last half-year, which was unsatisfactory for both sides."
Bayern are spoilt for choice in midfield with James Rodriguez also offering an option in a more advanced role following his arrival from Real Madrid on a two-year loan deal.
This summer, it has been suggested Bayern would be ready to cash in on Sanches if the right offer comes in. A report from Kicker in May suggested Ancelotti unconvinced the youngster will make the grade at the Bavarian giants, listing United as one of the clubs interested if they can recoup the initial €35m (£30.6m, $39m) they paid Benfica last year.