Ullrich wrote in his blog on Eurosport that "everyone can make his own opinion about what happened in cycling and I also contributed my role in that," but added that he would not make any public confessions like Armstrong, who was stripped of his seven Tour titles.
The German won the Tour in 1997 and finished runner-up five times, three times behind Armstrong.
Ullrich was suspended in 2006 in the fallout from Operation Puerto in Spain. He retired a year later. The Court of Arbitration for Sport banned him for two years in 2012 for involvement in the doping program of Spanish doctor Eufemiano Fuentes.