Star flyhalf Johnny Sexton is in doubt for Ireland's Six Nations opener against Wales after suffering another concussion.

Sexton, who missed three months of action after suffering four concussions in quick succession in 2014, was taken off during Leinster's defeat to Wasps last Saturday when he clashed heads with opposing centre Brendan Macken.

The influential pivot will now need to get through the necessary return to play protocols before being cleared, and on Monday he trained separately to the Ireland squad preparing for their Six Nations opener.

In a column for the Irish Independent, respected pundit George Hook said the latest head injury should not be overlooked.

'Johnny Sexton's concussion could be catastrophic for player, province and country. This is no ordinary brain injury,' he wrote. 'Sexton's history in this area is deeply worrying for everybody concerned about the well-being of this young man … The latest brain injury could be career-defining for Ireland's No 10 and will not easily be overlooked by him passing the protocols.'

Photo: Laurence Griffiths/Getty Images