Peter O’Mahony says Ireland must swiftly forget about the loss of the “exceptional” Caelan Doris and focus on executing a “seamless” back-row reshuffle. Leinster number eight Doris was tipped to shine in this year’s Guinness Six Nations but prematurely left the Irish camp after suffering with concussion symptoms.The enforced absence of the 22-year-old, who was arguably his country’s standout performer in the Autumn Nations Cup, presents a major dilemma for head coach Andy Farrell ahead of Sunday’s tournament opener away to Wales.