England international Sam Johnstone has been the Baggies undisputed number one this season – but the 28-year-old is currently serving a three-match suspension after picking up a red card against Cardiff.
Albion also have talented shot-stopper Alex Palmer on their books – a player who returned to the club in the summer following successful loans with Plymouth and Lincoln.
But it was Button who got the nod to start the FA Cup clash with Brighton on Saturday – with the former Fulham man making a number of impressive saves.
And Ismael believes the 32-year-old deserves to start the next two games for the patience he has shown this season.
“When you get a red card you lose a player but it’s always a chance for another one,” the boss said.
“Now it’s a big chance for David to step up because he deserves it.
“It has not been an easy situation for him but he has dealt with it really well, he is always professional and he has trained well.
“I think when you are a number two in a squad you need to be mentally strong – normally they’re stronger than other players because they need to deal with frustration.
“David did it perfectly so far and now is his chance.
“We have no concerns about that position. We know we have a very good keeper in that position and now it’s David’s time.”
As well as Johnstone, Button and Palmer – Albion also have England under-21 international goalkeeper Josh Griffiths on their books – with the youngster currently enjoying a loan stint in League One with Lincoln City.
With Palmer having barely featured this season, Ismael was asked if he too could secure a temporary move away this month.
And the boss said that is something they make look at after the Peterborough game.
“There are lots of scenarios – it’s one possibility to keep Alex because now he will be on the bench,” Ismael said.
“And you never know after that but now it’s clear that if all the keepers are in we have to assess the situation and what makes more sense for us.
“Because we have very good keepers for the short term and especially for the long-term.
“I think West Bromwich in the keeper position is very young and have big hopes.”
Meanwhile, former Albion boss Slaven Bilic has had his contract with Chinese Super League side Beijing Guoan terminated by mutual consent.
In a statement, the club said the Croatian wanted to return to Europe to be with his family during the ongoing coronavirus pandemic.
Bilic joined Beijing Guoan on January 6 last year, just three weeks after he was controversially sacked by Albion.
Despite financial issues behind the scenes, he led the team to a fifth placed finished in the Chinese Super League.
But the season ended last Tuesday. And despite initially signing a two-year-deal with the club, Bilic has opted to leave Beijing after just 12 months.