Jockey Michael Walker will undergo surgery for a back problem which is expected to keep him out of the saddle for three months.

Walker had to be helped off a horse after a race at Moonee Valley last Friday week when his back seized up.

He was forced to miss a feature Randwick meeting the following day and hasn't ridden since.

Walker's rider's agent Ryan Roberts posted on Twitter on Monday the jcokey would undergo surgery next week.

"Michael Walker will have key hole surgery on his L4 and L5 next Monday and will be out for 12 weeks," Roberts said.

Walker had been the rider of the Chris Waller-trained Comin' Through who is the early favourite for Saturday's Group One Randwick Guineas.

Champion Hong Kong jockey Joao Moreira has been booked for Comin' Through in Saturday's Guineas.