Cox Plate runner-up Happy Trails won't race again this spring after showing signs of soreness following a track gallop on Wednesday.

Trainer Byron Cozamanis said the horse pulled up a little bit "proppy" following his workout and would undergo further tests to confirm the extent of the problem.

Connections had been hoping to back Happy Trails up in Saturday's Group One Mackinnon Stakes at Flemington following his outstanding second to Shamus Award in the Cox Plate.

"It's very disappointing .... we were hoping he'd be right to run Saturday but that's the way it goes," Cozamanis told Sydney's Sky Sports radio.

"It's a bit sad but the horse will be all right, that's the main thing. He will come back after a spell and should be as good as gold."

Cozamanis was entrusted with the care of Happy Trails last week when the gelding's long-time trainer Paul Beshara was disqualified for six months after being found guilty of race day treatment of the horse.

Behsara was not granted a stay of proceedings pending an appeal.