Fiorente has won only twice from nine starts in England, where he was trained by Sir Michael Stoute.
The first victory came in a maiden at his second start, but his latest, in a 2400m group two race at Newmarket, earned him a A$1 million-plus price tag and a Melbourne Cup start.
In the Newmarket race he had Joshua Tree behind him in second place and last year's Melbourne Cup runner-up Red Cadeaux in third.
McDonald piloted Fiorente over 1600m at Werribee on Friday and gave the impression the potential identified by his trainer is emerging.
"He bowled over 1600m, worked into the corner really well and when I gave him a squeeze up the straight he extended like a really good horse," he said.
-AAP