Captain Caelan Doris and winger Tommy O’Brien have been ruled out of Ireland’s opening three fixtures in the Nations Championship due to injury, with hooker Dan Sheehan to lead the tour in Doris’s absence.The two players were withdrawn from Ireland’s squad for the upcoming games against Australia (July 4th), Japan (July 11th) and New Zealand (July 18th) on Saturday after sustaining injuries during Leinster’s 36-7 win over the Bulls in Friday’s URC final at Croke Park.Ireland head coach Andy Farrell had included the pair in a 36-man squad announced on Wednesday, but a foot injury for Doris and a groin issue for O’Brien will now see them sidelined for the southern series of the inaugural competition.Uncapped Ulster duo, brothers Bryn and Zac Ward have been called up in their places and will depart for Sydney with the rest of the squad on Monday.Updated Ireland squadForwards (20): Tadhg Beirne, Billy Bohan*, Thomas Clarkson, Jack Conan, Tadhg Furlong, Sam Illo*, Cormac Izuchukwu, Sean Jansen*, Rónan Kelleher, Jeremy Loughman, Joe McCarthy, Darragh Murray, Tom O’Toole, Cian Prendergast, James Ryan, Dan Sheehan, Tom Stewart, Nick Timoney, Josh van der Flier, Bryn Ward*.Backs (16): Bundee Aki, Rob Baloucoune, Harry Byrne, Craig Casey, Nathan Doak, Ciarán Frawley, Jamison Gibson-Park, Robbie Henshaw, Hugo Keenan, Stuart McCloskey, Jimmy O’Brien, Jamie Osborne, Sam Prendergast, Garry Ringrose, Jacob Stockdale, Zac Ward*.*uncappedFixturesSaturday, July 4th: Australia v Ireland; Allianz Stadium, Sydney, 11.10am Irish timeSaturday, July 11th: Japan v Ireland; McDonald Jones Stadium, Newcastle, 11.10am Irish timeSaturday, July 18th: New Zealand v Ireland, Eden Park, Auckland, 8.10am Irish time