The 22-year-old is currently on a season-long loan at Ibrox from Cardiff City and has impressed for the Gers, scoring two goals and providing two assists in 10 appearances.
Leeds were linked with a move for two-cap Wales international John last month.
The left-back position has proved problematic for the Whites since the departure of Charlie Taylor to Burnley.
John is out of contract at the end of the season.
Cardiff are considering cutting short his loan spell when the transfer window reopens and cashing in.