André Onana is expected to be sold and questions remaining over the future of 22-year-old Radek Vítek.
Journalist Alan Nixon reported that the 33-year-old Wolves goalkeeper is being considered as a back-up or third-choice option behind Senne Lammens, who is established as the undisputed number one under head coach Michael Carrick. Johnstone's contract at Palace expires at the end of June, making him available as a free agent.
Johnstone came through Manchester United's academy before leaving the club and spending time at a succession of English clubs — Aston Villa, Middlesbrough, Preston, West Bromwich Albion and Crystal Palace — before establishing himself as a Premier League goalkeeper at Wolves and earning senior England caps. He has 14 international appearances to his name.
Onana spent last season on loan at Trabzonspor and United are hopeful of selling him permanently this summer rather than reintegrating him into the squad. Vítek, who had a productive loan spell at Bristol City last season, faces a decision about whether to take another loan or move permanently — with clubs expected to register concrete interest.
United's Champions League return means goalkeeping depth will matter more than it did in 2025-26, with a significantly more demanding fixture list requiring Lammens to be supported by at least two credible alternatives.