Sean St Ledger is out of the Republic of Ireland’s opening World Cup qualifier with Kazakhstan because of a knee injury.

The Leicester City player suffered a medial ligament strain in a friendly with Burton Albion on Wednesday and has been ruled out for six to eight weeks by his club.

West Ham defender Joey O’Brien has been called up as St Ledger's replacement.

Ireland’s first World Cup qualifier is on 7 September in Kazakhstan.

St Ledger is also a major doubt for the double-header with Germany and Faroe Islands in October.

It is another blow to Giovanni Trapattoni, with Richard Dunne's groin complaint meaning the Aston Villa defender is also unlikely to feature in the first qualifier.

Leon Best suffered a serious knee injury last week that rules the striker out for at least the rest of 2012.