The John Gosden-trained colt, who has won three Group Ones over a mile and a quarter on his last three outings, is owned by Sheikh Fahad al Thani’s Qatar Racing Ltd, a subsidiary of Qipco who sponsor Champions Day.
Roaring Lion has not run over a mile since finishing fifth in the 2000 Guineas in May before he went on to win the Dante Stakes at York.
Listen to snap analysis of Roaring Lion's Juddmonte International triumph
As over 40 millimetres of rain fell at Ascot at the weekend, the ground is predominantly heavy on the round course while the Queen Elizabeth II Stakes takes place on the straight mile, which is currently soft, heavy in places.
Roaring Lion has a preference for quicker ground, which has had a bearing on the decision.
Sheikh Fahad’s racing manager David Redvers said: “It’s been confirmed this morning that he’ll go for the QEII as unfortunately there’s no sign of the ground drying up to not have heavy in the description on the round course.
“Obviously it’s disappointing he can’t compete in the Champion Stakes, but all along we’ve know that while we don’t have too much of a fear about him acting on soft ground, he’s got too good an action to have him flying through mud.
“Also, he seems to be more about speed this horse, he’s not a grinder – he’s got a serious turn of foot. I don’t think there’s any question now he’s a faster horse than when he ran in the Guineas.
“He seems in remarkably good fettle.
“We just needed the weather to hold for one more week. It’s heartbreaking, but it’s the price we pay for running the meeting when we do, but there’s nothing we can do about it as we have to fit into the world calendar, not just our own.”