Glass Harmonium has always been a good racehorse, but now that he can breathe, he has every chance of being a much better one.

And if he has learned to get out of the barriers - as trainer Mike Moroney believes he has - he might even give opponents the calibre of More Joyous and King Mufhasa a run for their money in Saturday's Group One Toorak Handicap (1600m) at Caulfield.

"He's needed two lots of throat surgery, so it's no surprise he's had his troubles in the past," Moroney said.

Glass Harmonium's breathing difficulties came to light in the Australian Cup at Flemington last March when his regular rider reported after the race that the horse had been making "a terrible noise".

A procedure was performed but scar tissue subsequently formed over the horse's epiglottis and a second operation was required.

"We had that fixed and so far he's been as good as gold," Moroney said.

Prior to his aborted autumn campaign, Glass Harmonium had been one of the finds of 2011 when his promising Queensland winter campaign was followed by a couple of good placings in the early spring and a start in the Cox Plate.

But the race turned into something of a debacle for the grey.

"Things went badly wrong on Cox Plate day," Moroney said.

"He loaded fine and they were ready to jump when Damien (Oliver) took his blindfold off and other horses started playing up and were backed out of the gates."

Glass Harmonium duly threw away any chance by hopelessly missing the start and finishing 10th to Pinker Pinker, only to bounce back at Flemington a week later to win the Group One Mackinnon Stakes.

Glass Harmonium will be ridden on Saturday by James McDonald, the 20-year-old New Zealander who followed his stellar autumn in Sydney with a Group One win in Hong Kong.

He will retain the mount in the Cox Plate two weeks later with a decision still to be made on a Mackinnon Stakes start.

"The owners wanted a jockey to commit to both races and we're delighted to have James on board," Moroney said.

Glass Harmonium has drawn the outside gate in the 10-horse field on Saturday, but his natural inclination to lead should lessen any disadvantage.

"He's come on a lot since he ran fourth the other day at Caulfield and I'd be really disappointed if he didn't give horses like More Joyous and King Mufhasa a bit of trouble," Moroney said.

Despite her burden of 60kg, More Joyous is a $1.90 favourite with TAB fixed odds to win her ninth Group One race and register her 22nd victory in all.