John Bath is the new managing part-owner of reigning Australian Horse of the Year Weekend Hussler whose career is being threatened by a rare leg injury.

Former managing part-owner Jill Kewish has sold her 25 per cent share of the gelding.

The other owners of Weekend Hussler have increased their stake in the rising five-year-old while trainer Ross McDonald's wife Margaret has bought five per cent.

"We've just moved all the names as they appeared in the race book up one with Margaret added at the end," McDonald said.

McDonald was unwilling to comment on how much money changed hands over the sale of the 25 per cent share in Weekend Hussler who cost $80,000 at the Melbourne Premier Yearling Sale.

He has won 12 races - including seven Group Ones - and more than $3 million prizemoney.

However the leg injury is keeping the horse away from the racetrack and McDonald has opted for a course of shock wave therapy which vet Rob McGuinness began on Weekend Hussler a week ago.

"A professor from the US suggested we try it," McDonald said.

"Time will tell how the injury responds to it. It's all trial and error at the moment."

If Weekend Hussler does come back, he is not expected to race again until next autumn at the earliest.

McDonald said he tore the synovial pad from his off fore fetlock when he jumped a shadow during the running of the Australia Stakes (1200m) at Moonee Valley in February, finishing fifth as odds-on favourite to Apache Cat.

The joint had become badly inflamed because of leaking fluid and the problem was discovered by an arthroscope.