The 28-year-old was knocked unconscious just 13 seconds into the club’s 27-21 victory at Leicester Tigers on 14 April.
Horne joined Northampton in 2017 having previously played for the Super Rugby side Waratahs. He was also a regular for the Australian national side, winning 34 caps and being named vice-captain alongside Michael Hooper in 2016.
“After undergoing tests, leading neurological consultants from The Royal National Orthopaedic Hospital (Stanmore) confirmed that Horne has suffered career-ending nerve damage to his right arm,” Northampton said in a short statement.
Interim head coach Alan Dickens said: “This is absolutely tragic news, and has been devastating for every member of the squad and staff here.
“All our thoughts are of course with Rob and his family at this time. Rob is not only a world-class rugby player, but he's an exceptional man.”
Saints CEO Mark Darbon added: “Rob has been the ultimate professional in his time at Franklin’s Gardens, and shone on the pitch in what has been a difficult season for Saints,” commented Saints CEO Mark Darbon.
“This news has shaken everyone at the Club, and I’m sure all of our supporters will join us in sending our best wishes to Rob, his wife Simone and their two young children.
“Rob will always be a part of the Saints family and we will, of course, do everything we can to help him through his rehabilitation and transition in to the next stage of his life.
“On behalf of the club I would like to thank all the medical staff who have helped Rob so far, in particular the diligence and professionalism shown by the Saints and Tigers medical teams, who reacted quickly and could not have done more for him from the moment his injury was sustained.
“Rob has asked me to pass on his deepest gratitude for all of the messages of support he and his family have received, but would now like everyone to respect his privacy while they deal with this news.”
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