North Queensland centre Justin O'Neill has undergone emergency surgery on his spleen.
O'Neill was admitted to Canberra hospital on Sunday and had the operation a day after scoring a try in his 100th NRL match, the Cowboys' 22-26 win over the Raiders.
Cowboys officials confirmed the former Queensland and Australia representative was taken to hospital after a restless night, having apparently suffered the "severe" spleen injury during the game.
Spleen injuries can take up to six months recuperation, but the club said it was too early to speculate how long he'd be sidelined.
O'Neill's father Sean told ABC radio his son was struggling to breathing on Sunday morning.
"He's had a CAT scan done and he's got a ruptured spleen," he said.
"I spoke to him very briefly this morning and he was having a bit of trouble breathing."
O'Neill was considered an outside chance to be recalled by Queensland for the State of Origin series opener on June 5, having last played for the Maroons in 2017.
"It's very disappointing, he's probably having one of his best years I think," Sean O'Neill said.
Teammate Matt Scott's chances of a Maroons recall also appear over after the Cowboys prop partially dislocated his shoulder against the Raiders.
Scott will get scans and could be out from anywhere between two weeks and six months.
Australian Associated Press