Australian team doctor Peter Brukner issued a statement saying Hughes had further scans at St. Vincent's Hospital during the morning and that his condition was unchanged from overnight.
The 25-year-old Hughes was batting for South Australia in a Sheffield Shield match against New South Wales at the Sydney Cricket Ground on Tuesday when he was knocked out by a delivery by Sean Abottt.
Hughes was treated on the field by medical experts, including doctors who were flown by helicopter onto the ground, before being taken to the hospital.
"Phillip is receiving the best possible medical care," Brukner said.
The match was cancelled almost immediately and other Sheffield Shield matches in Brisbane and Melbourne were called off Wednesday after consultation between Cricket Australia and the Australian Cricketers' Association.
Hughes was wearing a batting helmet, but the area behind his ear was unprotected.
Images of the hard-to-watch blow were broadcast almost instantly across Australia, and messages of support flowed in from around the world all night and into the morning. News channels were live at the hospital in downtown Sydney, where satellite TV trucks and dozens of news crews reported regular updates on Hughes' condition.
Hughes has played 26 test matches for Australia since his debut in 2009 but hasn't been able to earn a regular spot in the starting lineup. He was highly regarded by teammates and rivals, and regular fans who appreciated his no-fuss approach to the game.
The injury sparked debate about short-pitch bowling in the game, and the level of protection offered by contemporary helmets.
Cricketers didn't start wearing protective helmets until the late 1970s, when batsmen decided it was time to protect themselves against a 156-gram (5 1/2-ounce) hard leather ball travelling at up to 160 kph (100 mph).
Bouncers, where a fast bowler aims to push the batsman back toward the stumps with a ball that lands halfway down the pitch and rears up above chest or head height, are still a regular and acceptable part of the game.
The International Cricket Council revised its laws on short-pitch bowling in the early 1990s, putting restrictions on the number of short-pitch balls allowed per over to stamp out bowlers merely using the delivery to intimidate batsmen.
Former test bowler Brett Lee said Abbott did not deserve blame for the incident.
"You're always on edge bowling fast or being out there batting," Lee said. "When you see something as shocking as this you really feel for Phil. I know first-hand that no one goes out there to try and maim a batsman."
Speaking on Australian radio, cricket great Shane Warne called it a freak accident.
"It's a tough situation for everyone," Warne said. "You just think about how many lives the helmet has saved over the years. This is just one of those things."
Adding some optimism to Hughes' recovery hopes was Phil Simmons, a former West Indies batsman who recovered fully from a similar head injury and returned to test cricket.
Simmons was hit by a fast delivery by David Lawrence in a tour match for the West Indies against Gloucestershire in Bristol, England, in 1988. His heart stopped after the accident, but he made a full recovery after extensive brain surgery.
Simmons, who was also 25 at the time, was not wearing a helmet.
"I think there's an omen somewhere that he will pull through and I hope so," Simmons told the BBC. "My injury was as serious as you can get. I had to have emergency surgery to have a clot removed from my brain. I was written off as never to play again and put in a long-term unit for head injuries, but I was out in eight days."