Martial took the Premier League by storm after signing for Manchester United from Monaco in 2015.
His exploits under Louis van Gaal prompted many to think he could take his game to the next level under Mourinho's tutelage.
However, the France international has endured a nightmare season, managing just eight goals from 42 appearances.
Mourinho has been publicly critical of the 21-year-old in a bid to spur him on to rediscovering his best form.
But, behind the scenes, United look as if they are planning for life without the youngster.
Anthony Martial pretends to be a mannequin while on shopping trip Tue, April 25, 2017
Anthony Martial is spotted having some fun while out and about with girlfriend Melanie Da Cruz Pires in Manchester city centre
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Anthony Martial is seen pretending to be a mannequin while shopping on Monday
Anthony Martial could leave Manchester United if they sign either Ivan Perisic or Willian
Reports claim that the club harbour hopes of signing Inter Milan winger Ivan Perisic, while Mourinho is also keen to be reunited with Chelsea winger Willian at Old Trafford.
And The Independent claim Martial could be shown the exit door if the recently crowned Europa League champions manage to bring in any reinforcements in his position.
While the club's official stance is that Martial is not for sale, Mourinho will supposedly be more open to offers if he manages to lure either Perisic or Willian to United.
The report adds that negotiations for Perisic have currently hit a snag.
Anthony Martial could leave Manchester United if they sign a winger, reports claim
Inter Milan star Ivan Perisic is being backed to join Manchester United
United want to do a deal for around £30million, but Inter are holding out for £50m - a price tag Mourinho is currently not willing to meet.
Willian, meanwhile, appeared to rule out a move away from Chelsea last week by emphasising how much he loves living in London - and how much he wants to stay.
"London is a city I fit in very well," he told Brazilian outlet Globo.
"Before I even lived here I already liked it. Always in my free time, when I did not play here I would come here.
"Now I’m going to be four years living here."