Synchronised is the early favourite to win one of racing's most famous events but McCoy, who broke his duck at the National on Don't Push It in 2010, is not so sure how the thoroughbred will fare.
"I've ridden horses round Aintree that I didn't look forward to riding and they've jumped very well, and I've ridden horses round there that I thought would be brilliant and they've been anything but," said McCoy, writing in the Daily Telegraph.
"Some horses take to it and some horses don't. The only way you find out is by running them.
"He's a really tough horse and he tries, he has surprised us a lot in the past so he might have one more up his sleeve."
Saturday's much-anticipated race goes off at 4.15pm.