Gareth Southgate will announce his 26-man squad for the delayed Euro 2020 competition today.
And Albion goalkeeper Johnstone is expected to be included after it was confirmed Burnley’s Nick Pope is due to undergo knee surgery in the next few days.
Despite the Baggies relegation from the Premier League, Johnstone has enjoyed an outstanding campaign between the posts.
His impressive form saw him earn a call-up to the senior England squad for the first time back in March.
And outgoing Albion boss Allardyce believes the 28-year-old is more than ready to be part of an England squad competing at a major tournament.
“Sam Johnstone is one of the best goalies in the Premier League for sure, without any question of a doubt,” the former England boss said.
“I worked with Pickford at Everton, who’s now the England No1, and he’s right up there.
And with all the other goalkeepers I’ve seen, and you can mention all the foreign goalkeepers too, he’s right up with them.
“His distribution has also got better and better. He’s good enough to be in that England squad. He’s certainly good enough to go to the Euros.”
Johnstone has enjoyed a very consistent season in Albion’s goal.
That has led to speculation he could leave the club this summer with West Ham, Tottenham and Leeds amongst the clubs who are believed to be keeping tabs on him.
According to reports, Albion will demand £20million for the former Manchester United youngster.
But despite Johnstone’s fine form, he was at fault on Sunday when he let in a soft free-kick from Kalvin Phillips during Albion’s defeat at Leeds.
That match could turn out to be Allardyce’s last as a manager with the 66-year-old having now left his role as Baggies head coach.
But while Johnstone’s error allowed Leeds to extend their lead, Allardyce refused to criticise the keeper.
“He was allowed that mistake,” the Dudley-born boss said.
At the end of the day it didn’t cost us anything.
“The goalkeeper is the only man who can’t really ever make a mistake.
“I’m going to have to go a very long way to think about the last mistake Sam made.
“I can’t really think of one – that’s how long it’s been.
“He’s been very consistent.”
Elsewhere, Baggies duo Dara O’Shea and Callum Robinson have been named in the Republic of Ireland squad as they prepare for an international double-header in June.
Ireland play friendlies against Andorra on June 3 and Hungary on June 8.