The centre-back, who has enjoyed an excellent start to the new season, was forced off as Stephen Kenny’s side fell to defeat against Portugal on Wednesday.
O’Shea underwent a scan in Dublin following the game.
But he has now returned to Albion where they will carry out their own assessment.
It means the defender will not feature for his country in their World Cup qualifiers against Azerbaijan today and Serbia on Tuesday.
In better news for both the Baggies and the Men in Green, Callum Robinson has been added into Kenny’s squad.
Robinson tested positive for coronavirus before his side’s triple-header of fixtures.
It is the second time he has tested positive for Covid-19 having also contracted the virus back in November.
O’Shea’s injury is likely to add to Albion’s woes at centre-back.
The Baggies already have Matt Clarke out with a hamstring issue – with the Brighton loanee expected to be on the sidelines for another four weeks.
Both Clarke and O’Shea have enjoyed fine starts to the 2021/22 campaign.
But in Clarke’s absence, Semi Ajayi was restored to the starting line-up for the game at Peterborough and responded by scoring a stoppage time winner.
Prior to the start of this season, the Nigerian international had been a mainstay in Albion’s back line.
And Ismael was impressed with the way Ajayi responded to being left out the team.
“I was really pleased,” the boss said when asked to assess Ajayi’s performance at London Road.
“I know it’s not easy at the beginning when you don’t play but I’ve said we will need every player – every player will have their part.
“Some will get that opportunity quicker, some will have to wait a little longer.
“But the important thing is to stay focused and when your time comes try and help the team to stay on the right way and to have success.”
While the injuries to O’Shea and Clarke are a concern for the Baggies, Ismael is well-stocked at centre-half.
Alongside Ajayi, the Baggies are also able to call upon Cedric Kipre who impressed in the Championship for Wigan during the 2019/20 season.
Youngster Caleb Taylor is also highly thought of at The Hawthorns.
While wing-back Conor Townsend has also impressed when asked to fill in at centre-back this season.