Castlzeberg may be top filly Habibi's toughest opponent in the New Zealand Derby, but the filly's trainer Donna Logan is delighted he's running.

Habibi is the $2.80 favourite for Saturday's Derby, despite suffering her first defeat in her six-race career behind Valbuena and Castlzeberg in the Avondale Guineas two weeks ago.

Castlzeberg, who heads to Danny O'Brien's stable in Victoria after his sale to OTI Racing during the week, will be taking her on again but Logan is glad the Bob and Jenny Vance-trained front-runner will be there to ensure a strong pace.

"Bob has said he will be going to roll along so it will be a true staying test," Logan told NZ Newswire.

"I definitely believe I have got a very good stayer in her and having him there should mean the best stayer wins."

His presence became especially important after Habibi drew barrier one, which could potentially cause traffic problems.

"There's going to be speed, so I envisage she will be two or three back on the fence," Logan said.

"She's usually in midfield or just in front of midfield so that should be fine."

Logan says Habibi has improved greatly from her Avondale Guineas run, her first in six weeks.

"She's one of those horses that improves with racing," she said. "She mentally changes and seems to strip fitter, happier, stronger, grumpier. Her personality comes out after each race stronger and is much more domineering.

"We're pretty pleased with her."

Habibi's chances were helped when four-time Derby winning jockey Vinny Colgan confirmed he would ride her rather than Filly of the Year series leader Fix, who will now be ridden by Mark du Plessis.

Habibi, Castlzeberg and Fix are the only runners under $10 in the TAB odds.