Jason Doyle has been ruled out for the rest of the season and will therefore miss Grand Finals in Elite and Premier Leagues for Swindon and Somerset.
Hospital checks have revealed that Doyle has broken a bone in his neck after crashing in the second running of the Final in the PLRC, and he is likely to be off his bike for up to two months.
Somerset promoter Debbie Hancock said: "The weekend started out so well, with us qualifying for the Premier League Championship Final. But, instead of celebrating, we are having to come to terms with the fact we will be contesting both that and our League Cup Final without Jason.
"The hospital say that the break is not serious and he doesn't appear to have suffered any other damage apart from some bruising in the rib area. The break should heal naturally over the next 6-8 weeks, during which time Doyley will have to wear a neck support."
Doyle will be replaced by his Swindon doubling-up colleague Sebastian Alden for the first leg of the Elite League Grand Final between the Robins and Poole at Blunsdon on Monday.
Workington also have injury problems after their top two riders, Richard Lawson and Rene Bach, were involved in accidents on Sunday.
Bach crashed spectacularly in the Final of the PLRC at Sheffield and was ruled out of the Comets' 36-54 Knockout Cup semi-final first leg defeat at Newcastle later in the day, when Lawson also came to grief.
Manager Tony Jackson said: "After initially appearing to have escaped injury, Rene's right hand began to swell up quite badly on the way up to Newcastle, causing him considerable discomfort.
"Once at Newcastle he was deemed unfit to ride and we are grateful to Adam McKinna for agreeing to ride for us as a guest at less than one hour's notice.
"Then Richard Lawson fell at Brough Park, dislocating his right shoulder, and we will now have to assess the fitness of both riders ahead of another crucial weekend, which sees us contesting a must-win play-off fixture at Edinburgh on Friday and the second leg of the KO Cup semi-final at Derwent Park on Saturday."