Derby winner Masar will not race again this season because of a leg injury.
Part of Sheik Mohammed's Godolphin team, Masar beat odds-on favourite Saxon Warrior to win at Epsom in June and give trainer Charlie Appleby his first classic.
But he is thought to have hurt his leg in routine training on 6 July, the eve of the Eclipse at Sandown Park.
Godolphin say they want Masar to compete again next year, with Epsom's Group One Coronation Cup a target.
"Sheikh Mohammed is keen for Masar to run again at four," said Appleby. "If we are to deliver on that the best option is to give him a long break."