Guay said he hurt his back while landing after the 30-metre jump.
"That's ridiculous," Guay said. "Any course you should be able to push in the first training run and not have to worry about injuries like that."
The height of the jump was causing problems because racers land on a flat part of the slope, according to the skier Mont-Tremblant, Que.
"There's a little bit of a takeoff," said Guay, who called the rest of the Planai course "pretty fun."
"As long as it's a low flight and you land without big impact you can go 60-70 metres and no issue — we have that at other places in the World Cup," Guay said. "It's just the landing when it's too flat that everything comes into your legs and your back as shock absorbers."
Super-G world champion Ted Ligety, who will race downhill in the super-combined event on Monday, shared Guay's criticism.
"There are a couple of really big jumps onto really flat landings," the American said. "I'm always for big jumps but big jumps with flat landings are not that sweet. It's pretty harsh landing over those jumps."
FIS men's race director Guenter Hujara said course workers would try to slightly lower the jump ahead of Friday's second training.
"It's very difficult there. We can't take it down too far," Hujara said. "We have helpers on it and we'll see tomorrow morning."
More racers were unhappy with course conditions for the opening training, in which Hannes Reichelt of Austria posted the fastest time ahead of Italians Dominik Paris and Christof Innerhofer.
After overnight snowfall, the icy course was partly covered by spots of soft snow.
"It's tough, mostly due to the conditions," Aksel Lund Svindal said. "It's icy at some places and there are a lot of places where there is still a lot of bad, fresh snow that shouldn't be there. They'll have a lot of work to do on that."
The Norwegian, trailing leader Paris by three points in this season's World Cup downhill standings, expected a tough race.
"There's not that much gliding," Svindal said. "There are so many rolls that it doesn't feel like gliding."
Reichelt came down the 3.3-kilometre course in 2 minutes, 2.98 seconds. Paris was 0.11 behind and Innerhofer, the 2011 silver medallist , trailed Reichelt by 0.35.
Guay and Svindal finished fourth and fifth respectively, while last season's World Cup downhill champion Klaus Kroell was sixth. The rest of the field trailed Reichelt by more than a second.
A second training is scheduled for Friday, followed by the race on Saturday.
The course will be shortened on Friday as training takes place in between the two runs of the women's super-combined, which uses the same finish area.
The men will end their training at the point where the final intermediate time of the regular downhill is measured, effectively shortening the downhill run by just over 20 seconds.
Hujara said there will be an extra training run on the bottom part on Saturday morning, just hours before the actual race.
Canadian and Austrian coaches firmly criticized the lack of a proper second training run.
"Having a training run shortly before the most important race of the season is not good for the athletes," Austria head coach Mathias Berthold said. "They are victim of a badly organized race and training schedule."
The steep and turning finish section of the course is the most demanding part.
"I wasn't clean at some spots but it was OK for a first run," Reichelt said. "I tried to push a bit as we won't have the chance to ski the final part tomorrow."
Kroell said it's hard to pick the right line at the bottom section.
"It gets icier and bumpier further down the course," the Austrian said. "And the gates are set narrower there."
AP Sports Writer Andrew Dampf contributed to this report.