Horan sustained the injury during the captain's run this morning and was withdrawn from the Murrayfield showdown on Friday afternoon.

Ulster's Simon Best is promoted from the bench to loosehead with his provincial team-mate Bryan Young filling the vacancy among the substitutes.

Leinster winger Denis Hickie showed no adverse reaction to the back spasm that threatened to end his hopes of featuring against Scotland.

Hickie withdrew from training on Thursday with the problem and his fitness will be monitored until kick-off.

Geordan Murphy remains with the squad as cover with substitute Andrew Trimble set to win the number 11 jersey if Hickie is not given the all-clear.

Ireland are targeting a seventh successive win over Scotland with victory completing their third Triple Crown in four years.