12 months left on Man United contract
Johnstone has just a year left on his current contract at Old Trafford and that is likely to smooth over any deal that interested parties look to strike for Johnstone.
United will be keen to offload the goalkeeper now instead of losing him on a free in 12 months time, which will help negotiations as they are willing to sell their academy product.
That could help Celtic tie up a quick deal in time for their first game of the season on July 11, as they prepare to enter the qualifying stage of the Champions League in the second round.