Ryuichi Kiyonari has been forced to withdraw from the final round of the World Superbike Championship after succumbing to his painful injury during the opening day of action at Portimao.

The Ten Kate Honda rider broke his right collarbone in an accident last time out at Magny-Cours, the second time he has done so in a year, but while a clamp was keeping the bone stable, Kiyonari concedes he was in considerable discomfort during practice and provisional qualifying.

As such, the former British Superbike Champion has decided to curtail his season early, much to his disappointment.

“You can imagine that I am very disappointed to miss out on this final race of the season. I am especially sorry for my team, who have worked so hard this season. I would also like to apologise to Honda and the sponsors of the team.

“I wanted to race but, after I spoke with doctors and the team, we decided that it was not possible. It's a shame to end the season this way but now I want to get my shoulder fixed so that I am fit again for next year.”

Kiyonari's withdrawal brings an end to a difficult season for the Japanese rider, who was considered a title threat in 2009 following a debut year in which he won three races for the Ten Kate Honda team. Although he has stood on the podium twice – at Monza -, Kiyonari admits he has struggled to get comfortable on the bike.

Furthermore, following the announcement that Ten Kate Honda has signed Jonathan Rea and Max Neukirchner to its team for 2010, Kiyonari is so far without a ride next season and has been tipped for either a return to BSB, or to his native Japan.