Australia batsman Phil Hughes is in a critical condition after being hit by a bouncer at the Sydney Cricket Ground.
The South Australia left-hander, 25 collapsed after a delivery from New South Wales bowler Sean Abbott struck him on the head, missing his helmet.
Hughes was carried off on a stretcher and taken to hospital where he was put in an induced coma following surgery
Cricket Australia team doctor Peter Brukner said there would be no update on his condition until Wednesday.
Hughes, who has played 26 Tests, made his Test debut at the age of 20 against South Africa in 2009.
In only his second match, he became the youngest batsman to post two centuries in a Test match.
He played county cricket for Hampshire, Middlesex and Worcestershire and shared in a then world record 10th-wicket partnership of 163 with Ashton Agar against England in the 2013 Ashes series.
Having returned to the one-day side against Pakistan in the United Arab Emirates last month, Hughes was in contention for a possible Test recall following reports that Australia captain Michael Clarke might be ruled out of the first match against India on 4 December.
But he was hit on the side of the head as he tried to turn away from a short ball by fast bowler Abbott at the Sydney Cricket Ground, and was immediately surrounded by opposition players and umpires, who called for help.
A helicopter arrived but Hughes, who had scored 63, was taken to Sydney's St Vincent's Hospital by ambulance and a doctor who treated the player at the scene accompanied him, Australian media reported.
The Sheffield Shield match was abandoned.
Peter Lalor, senior cricket writer for the Australian newspaper, told BBC Radio 5 live: "He looked stunned, put his head down, we assumed he was going to shake it off but he fell sickeningly into the pitch, his hands didn't come out to break his fall, and then we knew it was pretty serious.
"Possibly the worst part of it was they had to give him mouth to mouth in front of the members' stand because he wasn't breathing.
"He is one of the most respected and liked kids in Australian cricket, he doesn't have an enemy in the game, he's great company.
"I was there when he played his first Test. Phil and I talk quite a lot and we were chatting in the UAE about him playing and said to him he would probably get Alex Doolan's place and he said 'I don't want it, I don't want to see that done to Dools, he's my mate'."
Cricket Australia chief executive officer James Sutherland said: "Our thoughts and prayers are with Phil Hughes. We are also thinking of his family, team-mates and friends in the Australian cricket family.
"His welfare is our highest priority. We're also naturally concerned about all of those involved in today's game and will be giving them our utmost support."
Australia coach Darren Lehmann wrote on Twitter: "Our thoughts and prayers are with Phil and his family. He is a great fighter and a great young man."
