The Honda rider crashed at high-speed at the end of the main straight during the second session, leaping off the bike before it crashed into a wall.
Although he had to be removed from the scene on a stretcher, Marquez was given a clean bill of health in the medical centre, having escaped serious injury.
"Just after the hill on the straight I grabbed for the brakes but I closed the front," Marquez explained.
"I tried to save it but the bike was pulling me towards the wall so I jumped from the bike to avoid hitting it.
"I hit my chin hard and strained my neck quite badly, I also have some contusions to my right shoulder, arm and leg but other than that I'm OK.
"Thanks to all the medical team that were quickly on the scene to assist me. Now I need to rest and see how I feel later tonight and in the morning."
The incident left Marquez 14th on the timesheets. His team-mate Dani Pedrosa was only fifth quickest, a second off the Yamahas' lead pace.