Leading fancy Solwhit has been ruled out of the Ladbrokes World Hurdle on Friday week.
The six-time Grade One winner had been set to step up to three miles for the first time, but last-year's Champion Hurdle sixth will miss the Cheltenham Festival after failing to impress connections in a Monday morning workout.
Byrnes said: "He just wasn't firing on all cylinders so there is no point in going.
"It's disappointing, but it was something of an afterthought anyway. We gave him two pieces of work and they weren't satisfactory.
"It would have been interesting to see how he got on over the trip.
"It's doubtful he'll run again this season and I think we'll go chasing with him next season."
Solwhit, now seven-years-old, had finished second behind Hurricane Fly on his last three outings.
He was as low as 10-1 with the sponsors for the World Hurdle.