In the past getting the weight off Manawanui has been a problem for trainer Ron Leemon but the horse's recent lack of appetite has been a bigger concern.
The four-year-old went off his feed a week ago, a day after what was a pleasing gallop between races at Warwick Farm.
In the past couple of days, Manawanui has picked up but Leemon admits Cox Plate plans are in the balance.
"He has picked up a bit," Leemon said.
"But we don't know what's caused it. There doesn't appear to be anything wrong with him.
"We have pencilled in The Shorts as a starting point but that obviously means the Cox Plate is doubtful."
The Group Two Shorts (1200m) is at Randwick on September 22 just five weeks before the Cox Plate (2040m) at Moonee Valley.
The delay in Manawanui's spring program is the latest of a series of frustrations for Leemon since his sparkling form a year ago.
Manawanui won the Group One Golden Rose and ran a fighting second to Helmet in the Caulfield Guineas.
His test run over the Cox Plate course was a triumph in the AAMI Vase before he found the 2500 metres too far in the Victoria Derby.
His autumn campaign was aborted after three starts. He followed two seconds with a fifth in the Randwick Guineas in which took so much out of him he was spelled with a view to the spring.
His usually healthy appetite meant he put on 50 kilograms during his time off and the raceday gallop last week was designed to top him off for a possible return in Saturday's Warwick Stakes.
Leemon said as long as Manawanui continued to make progress and nothing was found to be wrong, his program would be adjusted to encompass races up to 1600 metres with the Emirates Stakes on the final day of the Melbourne Cup carnival looming large.
"That is a race we have seriously looked at," he said.
"But everything has to go right over the next couple of weeks."