The 26-year-old has an Irish grandmother and becomes available to play for his adopted country straight away. Given Ireland's lack of options in the position, he has gone straight to the top of the queue to back up Ross.
He will be joined at training by Fitzpatrick, hooker Sean Cronin, who will cover Rory Best after he picked up a knock against the Dragons on Friday, scrum-half Paul Marshall, out-half Paddy Jackson and wingers Craig Gilroy and Tiernan O'Halloran.
Despite the lack of full-backs available, there was no call-up for Munster's Felix Jones or Leinster's Ian Madigan, who both scored from that position at the weekend. Munster out-half Ian Keatley is another who can feel hard done by, having been overlooked once again.
Bent arrived in Ireland yesterday having had discussions with his compatriot, and new provincial and international scrum coach, Greg Feek, about what to expect.
He has been playing at tight-head prop in Taranaki's run to (New Zealand domestic competition) the ITM Cup semi-finals that came to an end at the weekend and has played Super Rugby for the Hurricanes, albeit primarily on the other side of the scrum.
Joe Schmidt described the move as a "needs-must situation" for Kidney and, having seen more of the 6ft 1in, 18-and-a-half stone Kiwi in action than most, he gave Ireland fans a flavour of what they can expect.
"I think they were just trying to keep their options open in terms of the injury count," the Leinster coach said.
"I guess he's in a needs-must situation if that's the way he's going to be used. I have seen a fair bit of him on video-tape, I think he scrums really well on the tight-head and has done really well in the ITM Cup in New Zealand and did a really good job against Canterbury last week.
"Canterbury probably set the standard with the likes of scrummagers like Wyatt Crockett and Ben Franks, both of whom have spent a fair bit of time with the All Blacks, so he's playing at that level, and a bit of Super Rugby, but more so at loose-head. He's propped against all the big-name props either in New Zealand, Australia or South Africa."
"I guess they're just trying to make sure they have a safety net. Declan Fitzpatrick was back on the field on Friday night -- I thought he did well in that first Test (in New Zealand) but they're not my decisions to make."