Enda Stevens is set to miss Ireland's crucial September World Cup Qualifiers.
In a blow to Stephen Kenny's preparations for games against Portugal, Azerbaijan and Serbia, the left back is expected to be out for up to six weeks.
Sheffield United manager Slavisa Jokanvoic confirmed the news as he said Stevens could undergo surgery on a recent knee problem.
"Enda will still be a few weeks out. We are thinking too about some surgery and at the moment, we still waiting for his comeback," said Jokanovic.
"We are thinking he can be available with us during the international break or it can be after the international break. We are thinking about 4-6 weeks."
The injury ruled the 31-year-old out of the Blades' season opener against Birmingham City, while he also missed their Carabao Cup clash with Carlisle United earlier this week.
Ireland are without a win after losing to Serbia and Luxembourg in March qualifiers, and travel to Faro to take on group favourites Portugal on September 1.
Kenny's Boys in Green can then look forward to back-to-back home games as they welcome Azerbaijan and Serbia to the Aviva Stadium on September 4 and September 7.
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