Having bounced back from defeat at the Cheltenham Festival with a brilliant display at Punchestown in the spring, Chacun Pour Soi was a red-hot favourite to make a successful reappearance at Sandown.
But while he cut out much of the running, Chacun Pour Soi was a spent force before the home turn and trailed home last of the five runners.
“Chacun Pour Soi was very disappointing,” Mullins said at Punchestown on Sunday.
“He’s very sore behind today. We are not sure what it is yet, but we said we’d give him another day to get over it as he only arrived in this morning.”
It has been a mixed weekend for the champion trainer after unleashing several of his stable’s big guns.
Like Chacun Pour Soi, Elimay and Kilcruit both suffered short-priced defeats, but Mullins did still manage to claim five Sunday winners at Punchestown and Cork combined.
He added: “We are so far behind this season with the dry ground. I was reading the other day that it’s the driest November around the Dublin area since 1942. That’s some statistic.
“I was wondering whether we were getting too precious with our horses, but the figures bear out and we can feel it in the ground every day you go out.”