Disappointment quickly turned to optimism for Craig Williams when he picked up the Australian Guineas ride on Minnesinger after a minor injury ruled his original mount Disposition out of the $500,000 race.

Group One plans for Disposition had to be shelved after he slipped over at the stables of trainer Wez Hunter on Wednesday morning just hours before acceptances.

It left Williams without a ride in the race he has won twice on Shamus Award (2014) and Miss Finland (2007).

However, some quick thinking by Williams's manager led to the jockey picking up the mount on the talented Minnesinger.

"We were excited to have Disposition going into this week's Guineas and unfortunately he had a mishap so it was really disappointing," Williams said.

"Fortunately enough for me, I've been able to pick up a really nice horse for (trainers) Lee and Anthony Freedman and most importantly the horse has drawn a great barrier (three)."

Disposition, a Group One placegetter in Perth, was second in the C S Hayes Stakes at his first start for Hunter and was considered one of the leading Guineas chances.

Williams said he felt for owner Bob Peters and the horse's trainer who had aimed Disposition at the Flemington feature.

Hunter reported the horse had taken some skin off when he slipped, an injury that could take up to two weeks to heal.

Minnesinger, a well-bred colt by Lonhro out of Serenade Rose, is backing up in Saturday's Group One contest after his close second to Guineas second favourite Alpine Eagle in the Autumn Classic (1800m) at Caulfield last weekend.

Williams rates the colt a winning chance in an even race.

"Alpine Eagle only just beat him so he (Minnesinger) is going to be very competitive in this Australian Guineas," Williams said.