The 50-year-old Brazilian, pictured right, and his 6-year-old son, Luca, the only two people on the plane, were taken to the Sao Paulo Hospital in Araraquara, a citrus-growing region about 220 miles (350 kilometers) north-west of Sao Paulo, shortly after midnight on Sunday.
X-rays revealed a fracture in the lumbar region, and Fittipaldi reported difficulty in moving his left leg, Dr Luiz Roberto Neves, the hospital's clinical director, said in a radio interview.
"By some miracle, Luca didn't have even a cut," Neves said.
Neves said Fittipaldi told doctors the motor stalled and the ultralight crashed into a swamp from a height of about 300 feet.
"It wasn't a forced landing. It was a crash," Neves said. "The swamp saved [them]. If [they] had fallen on solid ground, [they] surely would have been killed."Reuse content