After finishing third in the Dante Stakes at York and in the King Edward VII Stakes at Royal Ascot, Sir Michael Stoute's colt emerged as a leading contender for the season's final Classic when he impressed in the Gordon Stakes at Goodwood last month.
Andrea Atzeni partnered Crystal Ocean at York and Ascot, but looks set to ride the Roger Varian-trained Defoe at Doncaster.
Ryan Moore steered Stoute's charge to his Goodwood victory, but he will almost certainly be claimed to ride for Aidan O'Brien and Coolmore on Town Moor, leaving the way clear for Crowley to get the leg-up for the first time.
Crowley said: "I'm very happy. I rode the horse this morning, he went really well and I was very impressed.
"I've been lucky enough to pick up a couple of nice rides for Sir Michael this year and I'm looking forward to riding this horse at Doncaster."
Crowley has notably teamed up with Stoute to win both the Coral-Eclipse at Sandown and the Juddmonte International at York this season with Ulysses.
Crystal Ocean is a best priced 7-2 market-leader for the Leger on September 16.