The Robert Hickmott-trained seven-year-old was a head winner of the two-mile feature last year and has only raced twice since, winning a Listed event at Flemington in September before finishing fourth in a Group Three at the start of the month.
Part-owner Nick Williams tweeted: "Frankie Dettori will ride Almandin in Melbourne Cup."
Godolphin could still have two runners in the Melbourne Cup if last year's fourth Qewy can bounce back to his best in Wednesday's Bendigo Cup.
Hartnell is set to shoulder top weight at Flemington for Godolphin, but the Charlie Appleby-trained Qewy could also take his chance should he run well at Bendigo.
Appleby's travelling head foreman Chris Connett told www.racing.com: "It's all guns blazing for Bendigo and we'll see where we stand after that. Hopefully he goes and wins nicely at Bendigo and then that opens the door for Melbourne.
"If he doesn't, then that might close the door."
A total of 36 horses remain in contention for the Cup following the second acceptance stage on Monday.
Hugo Palmer's Wall Of Fire has moved to 24th in the order with only the winner of Saturday's Lexus Stakes able to push him out of the final field if there are no further withdrawals by Saturday evening. Willie Mullins' Thomas Hobson is now 26th.
One rider who will not be in action in the big race is three-times winner Damien Oliver, who had his appeal against a 20-meeting suspension rejected at a hearing on Monday.