Walker will be on the sidelines for the next four and a half months after his star pacer returned a positive swab to lignocaine, 3'-hydroxy lignocaine and norlignocaine after winning a NSW Breeders Challenge heat at Young in September.

After fronting a Harness Racing NSW stewards inquiry, Walker was found guilty of three charges.

He was disqualified for three months after pleading guilty to presenting a horse to race when not free of a prohibited substance.

He was then handed the longer disqualification for pleading guilty administering a prohibited substance.

Stewards took into account it was Walker's first prohibited substance matter after 46 years as a licensed trainer and the class three nature of the substance.

The two penalties are to be served concurrently.

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Walker was also fined $500 for failing to maintain his log book while Mister Rea was disqualified from the race and the placings have been amended.

Walker explained the discrepancy was from a cream he didn't realise would swab.

"He had lumps on after Bathurst that burst so we got some cream to put on him, it was sitting on the table and months later we put the same cream on him and it swabs apparently," Walker said.

"It's just a rub on cream, Neocort it's called, and that's all that happened."

Mister Rea hasn't raced since finishing third in the MIA Breeders Plate final on January 26.

Perrot would have liked him to head to the NSW Derby heats next week but he is still awaiting results of another sample before being given the all clear to resume racing.

"It's all out of my hands but he's ready to rock," Perrot said.

"I would have loved to have raced him this Friday (at Wagga) and if he went good enough we would have looked at the Derby but we just can't.

"We're just sitting on our hands waiting."

After winning his first six races, including the group one Bathurst Gold Crown, Mister Rea was placed in his next three starts.

It saw him among the nominations for the NSW two-year-old of the season.

A hoof injury ended his NSW Breeders Challenge campaign but Perrot is happy with how it continues to respond.

Perrot has driven the three-year-old in all of his nine starts and despite the circumstances behind the move is excited to have a horse like Mister Rea in his Coolamon stable.

"I'll never get one off anyone else, not of that ability anyway," he said.

"He's getting some one-on-one care he mightn't get anywhere else and he certains takes longer to work than any other horse I've ever had.

"He gets that little extra here and there."

Mister Rea's ownership also needs to be changed to reflect Walker's disqualification before he can return to the track.