Plymouth Devils rider Hynek Stichauer has decided to quit British speedway after suffering a crisis of confidence in the wake of a recent crash.
The Czech Republic rider was involved in an accidental collision with Devils team-mate Kalle Katajisto, which led to the Finn suffering serious injuries.
Devils co-promoter Ashley Taylor said: "Hynek has been suffering from a lack of confidence and has returned home.
"He will be taking a break from Premier League racing."
Taylor added: "We will be seeking the facility to use rider replacement to cover his absence and run with six riders for our final five league matches."
Meanwhile, Plymouth will also be without number one rider Mikkel Bech for Friday's home match against Sheffield.
Bech will be racing in the Danish senior championship, and the Devils have called up Newcastle's Richie Worrall as a guest replacement.