With McCoy in the saddle, the ante-post favourite and Gold Cup winner was put down after breaking his leg in a fall in the four mile, four furlong race.
Along with the loss of According to Pete, Synchronised's death has raised further concerns about the safety of the Aintree course and McCoy has admitted it has been a painful experience.
"It is no understatement to say that he was one of our favourite horses, and that's not just because he won a Gold Cup," McCoy said in his Daily Telegraph column.
"The loss of any horse is painful, but it makes it all the more painful because he was such a great horse. What happened is still unclear to all of us, but losing any horse remains the toughest, saddest part of the job of being a jockey."