Any sale is likely to rule him out of the Derby, for which he is the $6 equal second favourite.
Valbuena upset Derby favourites Castlzeberg and Habibi at $34 in the Guineas on Sunday but his owners, the Vela brothers, usually keep their fillies but can sell their colts so if the numbers add up this week his Derby campaign may be over.
While punters who backed him could do their Derby money cold, Fix made her first appearance in the TAB markets for the classic yesterday.
She is also rated a $6 chance after co-trainer Ken Kelso confirmed the Derby is now her main aim.
Fix still appears in the markets with "not nominated" in brackets next to her name as her connections are not required to pay the $22,500 late entry fee until next week.
"But we are going to the Derby," said Kelso.
"Obviously there is no point paying the late entry fee until we have to next week in case something goes wrong but, that aside, she will be starting."
Mark De Plessis has been engaged to do the riding, with Fix's regular summer rider Vinnie Colgan committed to long-term Derby favourite Habibi.
That raises the rare occurrence of the two favourites for the Derby being fillies, with Castlzeberg on the third line of betting at $8.
Fix leads the NZB Filly of the Year series and could lose that title to Soriano in the New Zealand Oaks two weeks after the Derby, which Soriano also targets.
But Kelso has not ruled out starting in both classics. "She will remain in the Oaks entries at this stage and it is possible she could start in both, but there is a lot to happen before then."
Kelso's outstanding mare Xanadu will head to the Westbury Classic on the Auckland Cup Day, with James McDonald in the saddle.
The champion jockey partnered Valbuena to victory on Sunday but even if the 3-year-old stays in New Zealand and contests the Derby he will need a new rider.
"I'd love to come back for Derby Day and defend the title I won last season with Silent Achiever but I am committed to riding Dundeel in Sydney that day.
"But I will definitely be back for Auckland Cup Day."