Having taken the plunge of moving to the Bundesliga as a teenager in 2017, Sancho soon established himself as a starter in Dortmund.
He has since emerged as one of England's rising stars and is now valued at around £100m.
Last summer Dortmund rebuffed approaches for the 19-year-old, who was also understood to have been happy to stay.
However, according to the Daily Mail, events that have transpired this season have left Sancho disillusioned and unsettled.
Last month, Sancho was fined £86,000 by Dortmund for returning from international duty later than was agreed.
Then only last weekend he was substituted after just 36 minutes in one of the biggest fixtures of the season against Bayern Munich.
Dortmund went on to lose the game 4-0, but Lucien Favre's decision to hook Sancho so early was scrutinised.
After it was initially thought the substitution may have been due to injury, Favre revealed this was not the case.
"He was not injured, he trained yesterday," Favre told press after the game.
"I had to go on what I was seeing and, to be honest, it was not good enough."
The incident is reported to have left Sancho weighing up his future.
The uncertainty surrounding the starlet's future has led to the likes of Real Madrid and Manchester United preparing proposals.
However, it's understood they will face serious competition from Premier League leaders Liverpool.
The Reds are running away at atop the table and may seek to consolidate their dominance with a stellar signing like Sancho.
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