Nick Blackwell is no longer sedated after being operated on to reduce swelling on his brain.
Blackwell suffered the injury last week in an ill-advised sparring session eight months after he spent a week in a coma following defeat to Chris Eubank Jr.
The retired Trowbridge fighter is reported to be in a stable condition but his condition is being monitored as he has yet to wake.
Blackwell collapsed after being stopped in 10 rounds by Eubank Jnr in March and was rushed to hospital where he was found to have suffered a bleed on the skull and put into an induced coma.
After being released from hospital, Blackwell hung up his gloves but the lure of the ring appears to have enticed him back.
The British Boxing Board of Control's Robert Smith said it was "beyond belief" that Blackwell was sparring again and promised an investigation into the circumstances surrounding the injury.
The incident happened without the knowledge of Blackwell's former trainer Gary Lockett, who had encouraged the fighter to get his trainer's licence if he wanted to remain in the sport.
"I can't believe the boxer he sparred with, and (the) coach or coaches involved, would ever allow Nick to spar when he's had a brain injury," Lockett said in a statement.
"In due course, I hope they are dealt with by the British Boxing Board of Control in the correct manner.
"We thought that was all going very well and while we knew Nick missed boxing, we obviously didn't realise the extent to which he missed it.
"I am deeply saddened by what has happened. Nick is not just an ex-boxer of mine, but also someone I consider to be a friend."
Eubank Jr wished Blackwell all the best when he heard the news about his former opponent over the weekend.
"Nick Blackwell is back in hospital, after he tried to start sparring again. He's a tough, tough kid, I know he'll get himself through it again," he tweeted.
"I honestly hope everything is OK and the procedure he's had is not a serious one."