Despite the Baggies struggles this season, Johnstone has enjoyed an outstanding campaign, with the 28-year-old having made more saves than any other keeper in the top flight.
Out of contract in 12 months time, a host of clubs are believed to keeping tabs on the shot-stopper with Albion now on the brink of relegation.
Tottenham, West Ham and Leeds have all been linked with a move for Johnstone, who is likely to want to stay in the Premier League. Manchester United are also understood to want to take Johnstone back to Old Trafford – the club where he began his career.
The Express & Star understands when United sold Johnstone to Albion, they negotiated a clause that led to the Baggies paying them a fee after they won promotion to the Premier League. They also included a sell-on clause, which will be reflected in the transfer fee Albion demand.
Ole Gunnar Solskjær looks set to sell David De Gea this summer. But with Dean Henderson set to become number one, Johnstone is unlikely to return to Manchester with the Preston-born star sure to want assurances over his playing time.
West Ham is a more likely destination with the Hammers on the hunt for a replacement for 36-year-old Lukasz Fabianski. Leeds, meanwhile, are believed to want an experienced glovesman to compete with 21-year-old Illan Meslier.
Tottenham will also need a keeper if they sell Hugo Lloris while Watford are also believed to be keen on Johnstone.
In the meantime, Johnstone insists he and his team mates are going to keep fighting to keep Albion in the Premier League even though the odds are stacked against them.
“We’ve tried to stay positive all season, and although we’ve had ups and downs, we’ve kept going and that’s what we must carry on doing now,” he said.
“We have to keep going until the very end.”