Italy’s Alessandro Petacchi is among the quartet identified along with Croatia’s Kristijan Đurasek and Slovenians Kristijan Koren and Borut Božič. 

They have all been notified of potential anti-doping rule violations by the International Cycling Union (UCI) and have also been provisionally suspended. 

Petacchi, who retired from professional cycling in 2015, has been suspended while the UCI investigates the "use of prohibited method" between 2012 and 2013.

His only victories during that time were three stages of Bayern-Rundfahrt in Bavaria, Germany.

Koren and Božič are under investigation for the "use of prohibited method" between 2012 and 2013, when the former rode for the teams of Liquigas-Cannondale and Cannondale, and the latter represented Astana.

Đurasek is under investigation for "use of prohibited method" in 2017.

The UCI notified the four cyclists of potential anti-doping rule violations based on information received from the law enforcement authorities in Austria.

"The UCI has also provisionally suspended the above-mentioned individuals pursuant to Article 7.9.3 of the UCI Anti-Doping Rules," a statement from the world governing body added.

"The UCI and the Cycling Anti-Doping Foundation (CADF), the independent body mandated by the UCI to define and lead the anti-doping testing strategy and investigations in our sport, have been in close contact with the sport and state authorities involved in the Aderlass investigation, in particular with the World Anti-Doping Agency and the Austrian law enforcement authorities.

"The UCI and the CADF will continue to cooperate with and assist all parties involved in these investigations but, in view of the nature of the ongoing investigation, will not make any further comment at this stage."

Koren is currently competing for Bahrain-Merida at the Giro d'Italia, while UAE Team Emirates' Đurasek is contesting the Tour of California.

As reported by Cyclingnews, both riders have been suspended by their teams and sent home.

Božič retired from racing at the end of 2018 and has since been working as a sport director for Bahrain-Merida, which confirmed the suspension of both him and Koren. 

The team said it has a "zero-tolerance doping policy" and "always carries out thorough medical checks (including biological passport check) of any new signed rider".

UAE Team Emirates said it hopes Đurasek "can prove he was not involved in the affair". 

"Should it be proven otherwise, he will be terminated immediately," the team added.

Earlier this week, Petacchi's former team-mate Danilo Hondo of Germany was fired from his role as a national coach for Swiss Cycling after admitting to blood doping during his career.

The 45-year-old confessed to being involved in the Erfurt blood doping scandal during an interview on German television channel ARD.

Coordinated raids were carried out at the International Ski Federation Nordic World Ski Championships in Seefeld in Austria and in the German city of Erfurt in February.

At least 21 athletes from eight countries and five sports – three winter and two summer – are suspected of blood doping after police in Germany and Austria launched a targeted operation against what it believes is a worldwide drugs network.

Five athletes were arrested in Seefeld, while German team doctor Mark Schmidt was detained in Erfurt.

As reported by Cycling Weekly, Hondo paid €30,000 (£26,000/$34,000) annually for Schmidt’s services.

He is said to have been named by the doctor, who is being questioned in custody.

Hondo claims his involvement with Schmidt dates from 2011 until the end of his career in 2014.

That was a period in which he represented Lampre-Farnese Vini and RadioShack-Leopard, now known as UAE Team Emirates and Trek-Segafredo, respectively, but had no major wins.

Two other cyclists, Austrians Stefan Denifl and Georg Preidler, have also previously admitted to their involvement in the blood doping scandal.

Austrian skier Johannes Dürr, whose revelations about blood doping in an ARD documentary sparked the raids, was also arrested as part of the investigation.