And with Keith Earls and Tommy Bowe also capable of playing a number of positions, it's Fitzgerald, a Lions tourist just two years ago, who missed out.
"Luke is very unlucky not to be going on this trip, but within the squad we have a number of guys who can play a number of different positions as well," said Kidney.
"Luke can play in a number of different positions. If you look at it, Marcus Horan and John Hayes are Grand Slam winners and Heineken Cup winners, Peter Stringer, Tomás O'Leary, Jenno (Shane Jennings), Kevin (McLaughlin), the list goes on."
Leinster back row Shane Jennings also missed out after an underwhelming performance in the defeat to France on Saturday.
While Leinster will be without 13 members of their first team squad, along with Nathan Hines who is part of the Scotland group heading out to New Zealand, they will be able to count on the likes of Jennings, Fitzgerald and Shane Horgan for the start of the RaboDirect PRO12, which kicks off with a trip to Swansea to take on the Ospreys on September 2.
Ireland squad for the World Cup:
Forwards: Cian Healy (Leinster), Tom Court (Ulster), Mike Ross (Leinster), Tony Buckley (Sale), Jerry Flannery (Munster), Rory Best (Ulster), Sean Cronin (Leinster), Paul O'Connell (Munster), Donncha O'Callaghan (Munster), Leo Cullen (Leinster), Donncha Ryan (Munster), Stephen Ferris (Ulster), Sean O'Brien (Leinster), David Wallace (Munster), Jamie Heaslip (Leinster), Denis Leamy (Munster)
Backs: Conor Murray (Munster), Isaac Boss (Leinster), Eoin Reddan (Leinster), Jonathan Sexton (Leinster), Ronan O'Gara (Munster), Paddy Wallace (Ulster), Gordon D'Arcy (Leinster), Brian O'Driscoll (Leinster, capt), Keith Earls (Munster), Fergus McFadden (Leinster), Tommy Bowe (Ospreys), Andrew Trimble (Ulster), Geordan Murphy (Leicester), Rob Kearney (Leinster)
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