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, who has played 26 Tests, collapsed after a delivery from New South Wales bowler Sean Abbott struck his helmet.
Hughes was carried off on a stretcher and an ambulance took him to hospital where he has undergone surgery.
South Australian Cricket's manager Tim Nielsen said "the outcome is unlikely to be known for 24-48 hours".
Players and officials rushed to help Hughes as he fell to the ground
Hughes, who shared in a then world record 10th-wicket partnership of 163 with Aston Agar against England in 2013, played for the one-day side against Pakistan in the United Arab Emirates last month.
He was in line for a possible Test recall following reports that Australian captain Michael Clarke might be ruled out of the first match against India on 4 December.
After being hit by the ball, Hughes put his hands on his knees before falling face first on to the pitch.
He was immediately surrounded by opposition players and umpires, who called for help.
A helicopter arrived but Hughes 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.
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."