Enda Stevens is out of Ireland's November internationals with England, Wales and Bulgaria due to a knee injury.
The Sheffield United defender sustained the setback in his club's defeat to Chelsea on Saturday and was ruled out after turning up at the Ireland team hotel for assessment.
Stephen Kenny has called Cyrus Christie into his squad as a replacement, but the news might pave the way for Matt Doherty and Seamus Coleman to feature in the same side.
Coleman is fit again after shaking off a hamstring problem and he impressed Kenny in Everton's loss to Manchester United on Saturday.
Before the Stevens news was confirmed, Kenny pointed out that Doherty filled in as a left sided centre half in an emergency against Wales last month.
The Dubliner had a long spell as a left back with Wolves earlier in his career and Kenny has indicated he is happier to stick with a back four rather than tweak his formation.
Ireland play England in a Wembley friendly on Thursday before taking on Wales in their Nations League rematch in Cardiff on Sunday with the visit of Bulgaria to the Aviva Stadium on Wednesday week completing the triple header.