An inquiry into the bug which infected 10 Spurs players just before a vital match has cast doubt on suggestions they were victims of food poisoning.
Spurs midfielder Michael Carrick was one of the players struck by illness
The players had eaten at a London hotel before the Premiership match with West Ham on Sunday, which they lost 2-1.
Tests on food and players have been carried out by the Health Protection Agency and environmental health staff.
But they suggest one person had a form of gastroenteritis which may have spread to the other players.
'No definite conclusion'
Dr Alex Mellanby, Consultant in Communicable Disease Control at the Health Protection Agency, said norovirus, a form of viral gastroenteritis, was found in a sample from one of those affected.
But he added: "No definite conclusion as to the cause of the outbreak can be drawn from this one result.
"Only after we have received the results from tests being undertaken on further samples will we be able to make any definite conclusions."
He said the person affected by viral gastroenteritis appeared to have been exposed to it before the stay at the Marriott Hotel in Canary Wharf, east London.
First team players including Michael Dawson, Edgar Davids, Michael Carrick and Robbie Keane were struck down with the illness - although all four played in the game.
The result helped north London rivals Arsenal to secure fourth place and a Champions League spot ahead of them.
The FA Premier League has since rejected Tottenham's request to replay the match.