Ulster's director of rugby Les Kiss has revealed that Iain Henderson could miss Ireland's defence of their Six Nations crown with a hamstring injury.

Henderson was expected to partner Devin Toner in a new-look second row, as Joe Schmidt's side adjust to life without the retired Paul O'Connell.

However, Kiss has suggested that the lock is likely to be out for some time.

"Iain's type of injury has historically been up to six months," Kiss is quoted by Newstalk as saying. "At this stage it doesn't look good in terms of the Six Nations."

Henderson was part of the Ireland team that lost 43-20 to Argentina in the Rugby World Cup quarter-finals.