Six Nations 2015: Sexton would be missed against Wales - Williams

Injury to Ireland fly-half Johnny Sexton would boost Welsh hopes of defeating the unbeaten Irish according to former Wales international Martyn Williams.

Sexton kicked 14 of Ireland's points in the 19-9 win against England, but left the field in the second half.

Williams, 39, says his recovery could be key to Welsh hopes.

"A big glimmer of hope is Johnny Sexton walking off [against England] holding his hamstring," he said.

"If he's not there they [Ireland] are definitely a different team."

Sexton was replaced by Leinster number 10 Ian Madigan against England.

Williams, who won 100 caps for Wales between 1996 and 2012, does not think Madigan is likely to have the same impact on what could be a key encounter in terms

"Ian Madigan's a fantastic talent, but he cannot run a team like Johnny Sexton does," said Williams

Wales kept their championship hopes alive with a 20-13 win against France in Paris.

They are third in the table behind England and leaders Ireland who they play in Cardiff on Saturday, 14 March.

England are ahead of the Welsh on points difference with Ireland the only side with a 100% record with two matches to go.

Williams believes Wales face their toughest challenge of the tournament to date when they take on Joe Schmidt's side at the Millennium Stadium.

"I think they [Ireland] are so tactically good," he said.

"Their kicking game is phenomenal with Sexton and Conor Murray at half-back and they'll have a fantastic line-out with Paul O'Connell running it, so they've got the fundamentals.

"They'll be tough but there's no reason why Wales can't beat them in Cardiff."