Volkstok'n'barrell has been diagnosed with an asthmatic complaint which trainer Donna Logan believes accounts for his below-par performances during the Melbourne spring.

The four-year-old is back home with Logan and co-trainer Chris Gibbs in New Zealand where he is recovering after being treated for the respiratory disorder

In the Sydney autumn, Volkstok'n'barrell beat Preferment to win the Rosehill Guineas and finished a close third in the Australian Derby won by Mongolian Khan.

He failed to register a placing in five Melbourne starts and returned to New Zealand after his 12th behind Mongolian Khan in the Caulfield Cup.

"He's lived all his life with plenty of fresh air off the ocean here at Ruakaka," Logan told NZ Racing News.

"He went from a clean environment to a box in Melbourne and all that dust there so it makes some sense.

"It's a very uncommon thing and the vets have treated him and in six to eight weeks he should be cleared.

"The Christmas racing will come up too soon for him. We'll just wait, but we will be looking overseas again with him at some stage."

His talented stablemate Hasselhoof, however, will race over Christmas as he tries to extend his unbeaten record beyond his four races so far.

"He'll run at Ellerslie in the middle of December and we'll assess things after that," Logan said. "He looks a million dollars."

Like Volkstok'n'barrell, Hasselhoof is by Tavistock, and his wins have been from 1400 to 2100 metres.