That now looms as a problem again.
"It is more or less in the same place at last season and that is not a good sign," said Purdon.
"So the next three or four days will be crucial.
"If he heals quickly then he could make the Kaikoura Cup and the New Zealand Cup would still be an option.
"But he is by no means a certainty to be there."
Even if Auckland Reactor returns to full health in time for the Cup, the race is looking a less inviting target with every race-night gallop.
He has now missed away badly in both his starts this season and those antics are doing nothing for his already once-stalled stallion career.
Purdon does have the option adopted by the connections of another speedster in Sir Lincoln, who may concentrate on the New Zealand Free-For-All three days after the Cup rather than the great race itself.
"But even then the free-for-all could be a race decided by the barrier draw so if he misses the Cup maybe his focus will be on Australia."
Auckland Reactor's problems have seen him drift out to $7.50 in the New Zealand TAB's Cup market and he is not the only problem child in Purdon's six-strong Cup assault.
Former Cup placegetter Sleepy Tripp seems to have lost all interest in standing-start racing and his trainer is considering pulling the pin on the Cup for an all-mobile campaign.
The one Cup contender Purdon is thrilled with, though, is Fly Like An Eagle, who would be his drive in the classic should Auckland Reactor pull out.
"He is working super well and he will go to the Flying Stakes at Ashburton." Stablemates Highview Tommy and Sushi Sushi are still on target for the Cup, whereas Major Mark is unlikely to be there.
The latest round of Cup musical chairs could see Jarcullembra as one of the big winners.
After starting the week ranked 18th he could well be inside the magical 15 who get to start in the Cup by the end of next week.
He trialled at Alexandra Park yesterday and could head to the Flying Stakes, followed by the Kaikoura Cup.
Meanwhile, the sole Australian entry in the Cup, Caribbean Blaster races at Melton on Friday night.