Italian race walker Alex Schwazer, the 2008 Olympic 50km champion, is being investigated once again for doping, the German National Anti-Doping Agency (NADA) announced on Monday.
The 41-year-old could be facing the third doping ban of his career.
NADA said in a statement that the blood booster erythropoietin (EPO) "was detected in both the athlete's urine and blood samples" at the German road race walking championships.
Nada said it had "initiated a results management proceeding" and "imposed a temporary suspension".
Schwazer served his first ban after testing positive for EPO before the 2012 London Olympics. He did not dispute the results of that test and retired.
He returned and qualified for the 2016 Olympics but was then found guilty of micro-dosing anabolic steroids. Because it was his second offence, Schwazer was banned for eight years.
He argued he was the victim of a conspiracy because of his whistleblowing but, after a series of appeals in Italian and Swiss courts, the ban was upheld and he missed the 2016, 2021 and 2024 Games.