United could be in the hunt for a new goalkeeper as David De Gea continues to be linked with a move to Real Madrid, and Jose Mourinho is reported to be keen on Hart.
Transfer dealings between the two clubs are rare, and it was thought that Hart moving to Old Trafford would be immediately dismissed by City boss Pep Guardiola.
However reports now claim that Guardiola has no concerns over Hart joining the Reds and has given the move the green light if United do step up their interest in the England international.
The likes of West Ham have been heavily linked, but would struggle to match City’s £25million valuation and the player’s wage demands, something that would not be a problem for United.
Any move for Hart will depend on De Gea leaving to join Real Madrid, with reports claiming the Spain international is selling his house in Cheshire with a view to returning to Spain.