The 24-year-old flanker, the son of Mike Ruddock, who coached GUINNESS PRO12 sides Leinster and Newport Gwent Dragons, played under Schmidt at the Irish province and has five caps for his country.
"Rhys Ruddock would have been selected but has been ruled out after fracturing his arm against Uruguay last week," Schmidt confirmed.
"The squad selection has been a long process with some very tight decisions.
"Some injured players who are getting close to full fitness have been included while others have missed out due to prolonged absence or lack of opportunity to demonstrate their full Test match readiness."
The 45-man training squad needs to be cut down to the final 31 by August 31.
The World Cup starts on September 18, with Ireland's first game against Canada the following day at the Millennium Stadium in Cardiff.
Ireland's World Cup training squad
Forwards: R Best (Ulster), M Bent (Leinster), J Conan (Leinster), S Cronin (Leinster), T Furlong (Leinster), C Healy (Leinster), J Heaslip (Leinster), I Henderson (Ulster), C Henry (Ulster), R Herring (Ulster), D Kilcoyne (Munster), J McGrath (Leinster), M Moore (Leinster), J Murphy (Leinster), S O'Brien (Leinster), P O'Connell (capt) (Munster), T O'Donnell (Munster), P O'Mahony (Munster), M Ross (Leinster), D Ryan (Munster), R Strauss (Leinster), D Toner (Leinster), D Tuohy (Ulster).
Backs: I Boss (Leinster), T Bowe (Ulster), D Cave (Ulster), G D'Arcy (Leinster), K Earls (Munster), L Fitzgerald (Leinster), C Gilroy (Ulster), R Henshaw (Connacht), P Jackson (Ulster), F Jones (Munster), D Kearney (Leinster), R Kearney (Leinster), I Madigan (Leinster), K Marmion (Connacht), F McFadden (Leinster), C Murray (Munster), J Payne (Ulster), E Reddan (Leinster), N Reid (Leinster), J Sexton (Racing Métro), A Trimble (Ulster), S Zebo (Munster).
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