Aidan O'Brien says he has learned from Mendelssohn's Kentucky Derby experience and will be better prepared next time he takes a horse to Churchill Downs.

The UAE Derby winner was attempting to become the first European horse to win the Classic on Saturday but torrential rain turned the dirt surface into mud.

The Bob Baffert-trained Justify handled the conditions best while Mendelssohn trailed the field when Ryan Moore opted not to push him.

After receiving a hefty bump coming out of the stalls, Mendelssohn and Moore were always on the back foot.

"We learned a lot. We prepared for normal dirt racing," O'Brien told ITV Racing.

"Everyone was of the opinion that if you didn't get a good start your race is over in those conditions..

"Because of the bad kickback when it rains it is demoralising for a horse.

"American horses would have trained on it before but Ryan even said when he cantered to the start he was uncomfortable because it was coming up underneath him.

"It was a total extreme and we weren't prepared for that.

"If we were in that situation again we might be a little more prepared.

"I think we are thinking of the (Breeders' Cup Classic) so it looks like a break now before two preps, wherever they may be, and then hopefully back for the Classic."