On Tuesday, at the Sydney Cricket Ground (SCG), Hughes was hit on the head by a Sean Abbott bouncer while batting for South Australia against New South Wales in a four-day match.
The 25-year-old left-hander was admitted to St Vincent Hospital in Sydney and later underwent surgery.
Australian team doctor Peter Brukner said Hughes was in critical condition. (Team India send wishes)
"Phillip Hughes sustained a severe head injury while batting for South Australia at the SCG today. Phillip was treated on the ground by Cricket NSW medical staff and transferred by Ambulance to St Vincent's Hospital," Brukner said.
"He subsequently underwent surgery and remains in a critical condition in the hospital's intensive care unit. Unless there is any significant change there will be no further updates on his condition until tomorrow.
"Phillip is receiving the best possible medical care. The thoughts of his teammates and the wider cricket community are with Phillip and his family and friends at this difficult time. We ask that you kindly respect the family's wishes for privacy," he added.