An outbreak of coughing has brought a halt to the all-conquering Aidan O'Brien's Ballydoyle training operation.

The brilliant Irish trainer has been forced to put his rampant Tipperary yard under wraps after stars like dual Derby hero High Chaparral and Hawk Wing succumbed to the virus.

Initially O'Brien hoped that the problem was confined to his older horses but results on the track at the weekend suggested otherwise.

On Sunday, O'Brien's top two-year-old Hold That Tiger started hot favourite for the Group One Phoenix stakes at the Curragh - but trailed in last with confirmation on Monday that he had coughed after the race.

O'Brien told The Racing Post newspaper: "We've tested the horses who ran on Sunday and the results of those tests haven't come back just yet but Hold That Tiger and Ontario are both coughing.

"Because of the situation here there is no point talking about plans for horses just now."

O'Brien will now send a team of older horses to York's prestigious three day Ebor meeting next week - a fixture he would normally attack with gusto.

Aside from this hiccup O'Brien has had another superb season, not least with Manchester United boss Alex Ferguson's Rock Of Gibraltar.

The colt equalled Mill Reef's record of six successive Group One wins in last month's Sussex Stakes at Goodwood.