Newcastle Diamonds rider Lewis Kerr, 25, from Snettisham in Norfolk, was in collision with another rider before hitting a fence at an event on Sunday.
He was airlifted from the stadium in Peterborough to Addenbrooke's Hospital in Cambridge and the event cancelled.
Mr Kerr's wife Jessie posted on her Twitter account that the rider was now awake and breathing for himself.
Mrs Kerr, who is five months pregnant, said: "Lewi is out of induced coma and is breathing for himself now and remains in critical care.
"This is amazing and although it's early days and we are not out of the woods by any means, it's a positive.
"Myself and family can't begin to explain what the support has meant these last few days.
"Every message, picture and donation has given us strength during the worst time of our lives."
A spokesman for the Newcastle Diamonds added: "In response to the overwhelming support received by Jessie and the Kerr family, they wish to let everyone know that Lewi is now breathing unaided after being taken off the ventilator.
"Doctors, however, have stressed that this does not mean that Lewi is out of the dark yet, and this is still a "very serious situation".
"Though he could not be in better hands than those of the magnificent staff of Addenbrooke's Hospital."
Mr Kerr joined the Newcastle Diamonds on loan from King's Lynn at the start of 2013.
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