Connections of Dartmouth accept they must go "back to the drawing board" after the royal runner failed to fire on Irish Champions Weekend.
Big things were expected of the Sir Michael Stoute-trained entire in the Irish St Leger at the Curragh, but he could only finish eighth behind Order Of St George.
Dartmouth is, however, still likely to get another chance this autumn to gain redemption.
John Warren, bloodstock and racing advisor for the Queen, said: "We could not find anything wrong after Ireland and it is a case of going back to the drawing board.
"There are no imminent options that we are focusing on.
"It is a bit of a head-scratcher as he is such a genuine horse and he has never run a race like that.
"I would have thought he would run again this season, it will be a case of just trying to find a race for him."