The Englishman, who arrived at Old Trafford in 2011, spent the 2016/17 campaign on loan at Championship side Aston Villa and impressed manager Steve Bruce, who has expressed interest in permanently installing him as the Clarets’ first choice keeper.
New Middlesbrough boss Garry Monk will lose both Brad Guzan and former red Victor Valdes this summer after their demotion to the Championship and is on the look-out for a new No.1.
And according to the Sun‘s Alan Nixon, Mourinho will be open to selling the 24-year-old for around £2.5m this summer.
Not every youngster that pours through the ranks at Old Trafford can be guaranteed a regular spot in the first team; what they can be guaranteed, however, is that a footballing education at Man United will lay a solid platform for a sustainable career elsewhere.
We have seen this recently with Josh Harrop, who signed for Preston North End last week, alongside the likes of Reading’s Tyler Blackett – so close to making a return to the Premier League under Jaap Stam.
And the same can be seen here with Johnstone. The keeper has found his calling in the Championship and, under the highly rated Monk, will fancy his chances of making a return to the Premier League next year.