Johnstone is currently on loan at Aston Villa, but United have the right to recall him, if they are able to sell him on permanently.
West Ham are now among the potential suitors for the England youth international, who is valued at £5 million, but Johnstone would be unwise to join David Moyes’ side.
Johnstone is playing regularly at Villa, and he has developed massively over the past 18 months.
At West Ham Johnstone would surely be consigned to playing a bench-warming role though.
West Ham already have Joe Hart on loan, while Adrian has been in fine form since being restored as Moyes’ side’s number one.
For Johnstone to waste time as a third choice stopper at West Ham simply makes no sense, and he would be far better off staying at Villa than moving to the Hammers in January.