Rathgar Beau was retired after suffering an injury on his return to action at Gowran Park on Saturday.
Dusty Sheehy's stable star travelled well in the Grade 2 National Lottery Agent Champion Chase but appeared to go wrong before the bend and Shay Barry pulled his mount up before the third last.
The 10-year-old was found to have suffered a recurrence of the injury to his off fore.
'If he was a younger horse I would persevere with him and patch him up but he's too old and it wouldn't be fair on him,' said Sheehy. 'We had some great days with him. We'll be lucky to get one as good as him again.'
Rathgar Beau's finest hour came in the 2005 Kerry Gold Champion Chase at Punchestown when he inflicted Moscow Flyer's first ever defeat in a completed chase when edging a tight photo finish.
Sir Oj ran out a convincing winner of the race, bouncing back to form on his first start of the season.
Paul Carberry hit the lead four out on the gelding and he forged clear before the third last.
Light On The Broom threw down a late challenge but never looked like pegging back the winner, going down by a length-and-a-half.
'He always runs fresh and jumped great. Having run in the National, sometimes they come back not the same,' said winning trainer Noel Meade.
'We won't over-race him and will probably keep him to races like this. He'll get an entry for the Paddy Power at Cheltenham and we'll see the weights. We don't want to have him giving loads of weight away.'
Sonne Cinq claimed the Langtons House Handicap Hurdle in good style, despite racing from 4lb out of the handicap.
Davy Condon produced the mare to lead between the last two flights and she soon settled matters, going on for a cosy length-and-a-half success over Yarra Maguire.
'I'm delighted as she was a little unlucky at Listowel,' said trainer Willie Mullins. 'I would like to get her listed placed as she has a nice pedigree.'
Colm Murphy was hoping that his charge Sher Why Not would 'be alright in the morning' after his success in the Gain Feeds Maiden Hurdle.
The gelding who has had 'so many things wrong with him' opened his account over hurdles when holding the late challenge of Badgerlaw by a neck.
Carthalawn gave a good display of jumping when making all for a convincing four-and-a-half length success in the Lord Bagenal Inn Beginners Chase.
22-year-old Dubliner Adam O'Neill partnered his first winner when getting Rusty Red home by a short-head from stable-mate Piltown in the opening Kilford Arms 3-Y-O Hurdle.
Monty Mint may be finished for the year after his victory in the David Flynn Construction Handicap Hurdle, with trainer Tom Foley describing him as 'a summer horse.'
Foley doubled up in the final contest when Giant Eagle made a winning debut in the second division of the bumper.
The Giant's Causeway gelding battled well in the closing stages to prevail by a length from Well Saved.
Sizing Africa made an impressive debut when taking the first division of the contest by eight lengths.
