VIENNA, March 4 (Xinhua) -- Professional cycling team Groupama-FDJ said Monday Austrian rider Georg Preidler has admitted to blood doping related to a case which began with the arrests of five skiers.

The team says Preidler offered "his immediate and spontaneous resignation, justified by his inexcusable involvement" in the doping case. He had allegedly undergone "blood collection" procedures twice last year.

Authorities in Austria previously said Sunday that another rider had admitted to doping and was suspected of sports fraud in connection with the case. Austrian media reports named the cyclist as 31-year-old Stefan Denifl, although he has not been officially identified.

The cyclist was arrested on Friday and released later the same day after pleading guilty to unspecified charges.

Austrian and German police mounted a series of raids on Wednesday into a doping ring thought to have been based in Erfurt in Germany and led by a 40-year-old sports doctor named as 'Mark S'.

Austrian and German police arrested nine people last week, including five cross-country skiers at the world championships and the German doctor.

Austrian authorities said they had disrupted an "international doping ring" with involvement in multiple sports. One skier was arrested part-way through a blood transfusion.

The five skiers arrested were two Austrians, Dominik Baldauf and Max Hauke, Estonians Karel Tammjaerv and Andreas Veerpalu, and Kazakh athlete Alexei Poltoranin.

The International Ski Federation (FIS) later announced all five had been suspended.

Footage posted on social media showed Hauke apparently caught red-handed with a needle in his arm during the police raid with an officer looking on.

The arrests led to the resignation of Austria's Nordic skiing coach Trond Nystad, who said he could "no longer motivate (himself) when such things happen".