Jump jockey Jason Maguire is recovering after back surgery on Monday aimed at helping him to continue his career.
The Irishman, who has not ridden since February, has been tipped to challenge for future champion jockey titles after the retirement of AP McCoy.
"It could be a week or two before he has a full prognosis of how it has gone," said Maguire's agent Chris Broad.
The 35-year-old won the 2011 Grand National at Aintree on Ballabriggs.
Before his operation, he told the Times: "If the surgery doesn't work, I'm not sure what more I can do to get back."
He endured a career-threatening injury in a fall at Stratford on the eve of last year's Cheltenham Festival, suffering internal bleeding, a fractured sternum and having part of his liver removed while in an induced coma.
"It's a separate problem from the first one, lower down the vertebrae," he said.
"I'm staying positive but I don't know how I can come back if they can't get this right. With AP gone, I thought I had a great chance to be champion but it's not to be - at least for now."