The 21-year-old has been told by the club hierarchy that he’ll struggle for playing time this season and it would be best if he sought regular first-team football elsewhere.
He was a January signing from Hamilton Accies and played regularly for his boyhood heroes as the 2017/18 campaign drew to a close.
However, he hasn’t featured in either of Rangers two European fixtures so far and appears to have dropped down the pecking order under new manager Steven Gerrard.
Sunderland boss Jack Ross is keen to offer Docherty the chance to play regularly at the Stadium of Light, where he’ll team up with former Hearts stars Jon McLaughlin and Alim Ozturk, along with ex-Hibs favourite Dylan McGeouch.
The Wearside club are favourites for the English League One crown after suffering relegation from the second tier last season.