Popular stayer Efficient, winner of the 2007 Melbourne Cup, has been retired after sustaining a leg injury.
The Lloyd Williams-owned gelding, who has been plagued by injuries throughout his career, had been due to run in either Saturday's Metropolitan Handicap at Randwick or the Turnbull Stakes at Flemington.
Williams' son and racing manager Nick confirmed the retirement of the nine-year-old in a tweet on Thursday following what was believed to be the recurrence of an old injury.
"Efficient has been retired after suffering a leg injury this morning," he said.
"Efficient will be retired to a five star paddock at our farm. He will have a very enjoyable retirement with his old mate Zipping."
Efficient burst to prominence during his three-year-old season winning the 2006 Victoria Derby.
He returned the following spring to give Williams and then-trainer Graeme Rogerson a memorable Melbourne Cup victory, becoming the first horse since Phar Lap to win Australia's greatest race a year after claiming the classic.
The grey looked to be on track for another shot at the Cup when he scored a last-ditch win in the Turnbull Stakes in October 2009 but injury struck and he didn't race again for almost two years.
Efficient has had to be carefully managed since but he did show a glimpse of his best when he beat all but Niwot in the Group One Sydney Cup during the autumn.
By Zabeel, the sire of two other Melbourne Cup winners - Might And Power and Jezabeel - Efficient raced 29 times for seven wins and just under $4.8 million prizemoney.