His Manly teammates call him Snake, but star fullback Brett Stewart doesn't care much for reptiles at the moment.

As he struggles for full fitness in the early rounds of the 2016 NRL season, Stewart revealed he has suffered an off-field blow that has left him "shattered".

The promising racehorse in which Stewart shared ownership has died from a snake bite.

Stewart said Zee Dana, a placegetter in the NSW Pacers Derby last, couldn't be saved despite the best efforts of vets.

"It was a tough pill to swallow," Stewart told reporters on Wednesday.

"All of us owners are shattered."

Stewart bought into Zee Dana last year on the advice of his roommate, Sky Racing commentator Gareth Hall.

The three-year-old won six of his 13 starts and was placed another five times.

"It was alongside 19 other horses - they were hopeless apparently, and it just attacked ours," Stewart said.

Zee Dana was Stewart's first interest in a pacer.