Newcastle Diamonds have confirmed that Slovenian rider Matej Ferjan was found dead at his home in Poland on Sunday.
The club also revealed the circumstances behind Ferjan's passing are still to be established by the Polish authorities.
"Everyone is shocked at this tragic news," the club statement read.
"The official cause of death is as yet unknown, and it would be inappropriate to comment on the rumours or speculation at this time."
"Since joining the Newcastle Diamonds, Matej was jovial and seemingly happy, which makes this even harder to comprehend.
"Newcastle Speedway sends its sincerest condolences to Matej's family and friends at this extremely difficult and tragic time.
"We will issue further information as and when it is appropriate to do so."
Ferjan joined Newcastle in April, having previously ridden in England for Poole Pirates.
He made over 100 appearances for the Pirates and was part of the squad that won the Elite League and Knockout Cup double in 2004.
Pirates boss Neil Middleditch told BBC Radio Solent: "It's a real sad day for speedway.
"He was as a quiet little character, who was fearless and certainly a great little rider, so it's very sad."