Major Mark has been sold to Perth and Auckland Reactor looks set to be retired after a dreadful run at Ballarat two weeks ago.
"I am not sure exactly what is going to happen to him, I think he might be retired to stud," Purdon told the Herald.
"His owners will decide that soon but he is definitely out of the series."
That left Purdon with just Highview Tommy, runner-up behind Terror To Love in the New Zealand Cup in November, as an Interdom candidate and he will return to Auckland instead.
"He simply didn't go well enough in the Hunter Cup to justify staying over here.
"So I will set him for the Auckland Cup instead, which looks a more realistic target."
The Auckland Cup is at Alexandra Park on March 8, five days after the Interdoms.
So Purdon, having started the season with one of the strongest open class teams ever, will be watching the final from the driver's room at Menangle.
There is better news on the trotting front though, with stable star I Can Doosit producing an improved performance at the trials at Melton on Monday night.
It was his first public outing since two shocks defeats in the north in December, after which he was treated for fetlock soreness.
"He started against the pacers and went well," said Purdon.
"He actually put in a rough stride at the 150m mark but I think that is because he was trying to go too fast."
I Can Doosit will race at Melton on Saturday week before spearheading the New Zealand team for the A$200,000 Glenferrie Farms Challenge at Menangle on Inter Final Day.
He was issued the first invitation of the five-strong New Zealand team for the new race and will be joined by stablemates Escapee and Dr Hook.
Stig was also issued an invitation but is still 50:50 to cross the Tasman, while the final Kiwi spot goes to The Fiery Ginga.