The 26-year-old crashed on the rail feature of the slopestyle run at Rosa Khutor Extreme Park, Norway team manager Thomas Harstad confirmed, and was taken to hospital with his neck secured in a brace.
"He landed on his face and his right shoulder," said Harstad.
Horgmo's accident follows a stream of criticism from competitors over the safety standards of the course.
"I saw that he fell over the rail and trashed pretty hard. He tried a really hard trick (switch hardway backside 270) — probably the hardest trick
you'll see all day. He was transferring from one jump to another rail," said Norwegian teammate Ståle Sandbech.
Sandbech said he could not give an opinion on Horgmo's condition.
"You never know when you crash. A crash can look bad and you're fine or the opposite but he's a tough Viking," he said.
After the accident, Horgmo, who missed the 2006-2007 season after cracking his spine, was placed in tarpaulin and carried down the course to the medical tent. He was seen flexing his hands as he was taken in for an examination.
Harstad said Horgmo, who is ranked third on the World Snowboard Tour for this season, was conscious but in pain and the extent of his injuries were not yet clear.
Ireland snowboarder Seamus O'Connor, who was out training in the same session as Horgmo, said he anticipated there would be injuries.
"The course needs some work. They overbuilt the jumps because they were anticipating that the snow would melt," said O'Connor.
"At the moment the riders are not happy. The rails up top are too close. The riders need to speak up about the conditions. The rails can't be fixed but they can fix the jumps."
Other riders on Monday complained about the course's three imposing jumps which get progressively larger with Canada's Sebastien Toutant comparing it to "jumping out of a building".
Riders met at the end of the three-hour training session, with America's Charles Guldemond drawing a map of the course on the snow on his board to suggest where changes were needed.
"The last jump has a lot of impact on it and the takeoff is really long. Some of the guys and girls are intimidated. I felt like I was dropping out of the sky," he said.
International ski federation's (FIS) assistant snowboard race director Roberto Moresi said tweaks would be made to the course, but absolved the design from being at fault for Horgmo's accident.
"He was just trying a really hard trick," claimed Moresi. "There are just some minor adjustments. We're making the kickers (the slope riders use to gain speed to do tricks on the features) tighter and making them thinner so riders can go around them."
Slopestyle, making its debut at Sochi, is a spectacular high-speed snowboard discipline.
Competitors perform on a slope featuring various forms of obstacles — rails, quarterpipes, and jumps.
Horgmo is credited with landing the first "frontside triple cork" on such a course.
Training resumes on Tuesday, qualifying in the men's event is set for Thursday with the finals on Saturday.