American BMX racer Connor Fields suffered a brain bleed during a horror crash in Friday's Olympic event but has been moved out of intensive care, according to his mother Lisa.

A message posted on Facebook on Saturday said the 28-year-old, who crashed in the third run of his semi-final heat, was "cogent and communicative when awakened."

Thanking followers for their "companionship and concern and prayers for Connor", Lisa Fields updated a previous message in which she said surgery was a possibility.

"Latest CT scan shows no additional brain injury and no additional bleeding so he has been transferred from ICU critical care to high level care and does not require surgery at this time," she wrote.

Lisa had written in the earlier message that tests showed Connor did not have internal bleeding or a spinal injury.

"Brain function evaluation is ongoing and I will continue to update as I know more and after I get to speak with him," she said in the post.

Fields was the reigning Olympic champion heading to Tokyo after his victory at Rio de Janeiro in 2016.

He had already qualified for the final before suffering a horrible fall in the first corner of his third run.

Fields underwent a CT scan on his brain Saturday morning, his father Mike Fields told USA TODAY Sports Saturday, adding Connor also had CT scans on his spine and abdomen.

"Cognitively, he's doing well," Mike Fields said. "He knows where he is. He knows his birthday. He recognizes people."

The Texan was competing at his third Olympics and was one of the big favourites for gold as the reigning champion.

In his absence Dutchman Niek Kimmann – himself involved in a scary crash when an official walked on to the track during training earlier in the week – took gold ahead of Great Britain's Kye Whyte.

Australian Saya Sakakibara also crashed heavily while in the lead of her women's semi-final on Friday.

Sakakibara, whose brother Kai missed the Olympics after suffering brain damage following a BMX crash last year, escaped with mild concussion symptoms.