It comes after new rules for the 2021 season forced club bosses to split up their initial side.
All clubs must now include a rising British star at reserve – but with none of the eligible racers included, the Parrys International Wolves have had to change their plans.
Uncertain travel arrangements have proven to be the key factor behind letting Thorssell go, who has ridden for the Monmore Green side every season since 2012.
Chris Van Straaten said: “It was always going to be a difficult one because we were the only Premiership side with a fully committed 1-7 who had agreed to ride in 2020.
“Every other club were going to have to make at least one change anyway it seemed and that’s what makes it more disappointing from our point of view.
“Whilst still not easy, our decision was kind of made for us in the end.
“Our other six riders will be based here in the UK once the season is up and running, whereas Jacob would be based back home in Sweden and commuting in and out of the country constantly.
“Both Jacob as an individual and myself as a promoter of Wolverhampton Speedway were very concerned with the current travel problems that exist in the world right now.
“And even when the season does get underway in May, the virus will still be in the background and that could immediately disrupt travel without warning at any given point.
“So with my other six riders, as a club we are a lot more comfortable knowing they will be based in the UK and it kind of puts us in the driving seat.
“Jacob’s constant commuting would’ve been a major worry and a risk – and that’s why we both came to that decision.
“I must emphasise that Jacob hasn’t turned his back on British Speedway at all and I would certainly like to think that Jacob will be back racing for Wolverhampton at some point in the future.”
Talks are ongoing regarding Thorssell’s replacement and the Parrys International Wolves will make an announcement in due course.