State Man has been ruled out for the season and will not bid to reclaim the Champion Hurdle title at Cheltenham in March.
Trainer Willie Mullins said the horse had suffered an injury on the gallops on Wednesday morning.
The eight-year-old was second to Constitution Hill in the 2023 Champion Hurdle and won the race the following year.
State Man was leading when falling at the final flight in last year’s contest but went on to win the Champion Hurdle at Punchestown.
He is a two-time Cheltenham Festival winner, having landed the County Hurdle in 2022.
Mullins told the Sporting Life: “Sadly State Man has suffered a tendon injury on the gallops here. He’ll definitely be out for the rest of the season.”