T-Mobile said it is also monitoring an investigation into former massage therapist Jef d'Hont's recent claims in his book that the EPO was supplied by the University of Freiburg clinic.
D'Hont worked for T-Mobile from 1992-96 when it was known as Team Telekom. Riis won the 1996 Tour and Ullrich finished second. Ullrich won the 1997 Tour.
D'Hont claims that team doctors Andreas Schmid and Lothar Heinrich administered EPO shots every few days to riders in their hotel rooms from 1992-96.
"After discussion with Doctors Heinrich and Schmid, we have mutually agreed to discontinue their personal provision of medical service during the course of these inquiries," T-Mobile general manager Bob Stapleton said on the team's Web site.
"We hope that the independent experts can clear the allegations, so that the cooperation can be continued."
The Freiburg district attorney's office has started an investigation into d'Hont's accusations, German media reported. Two doctors at the University of Freiburg clinic, plus the T-Mobile doctors, are believed to be the targets.
T-Mobile's management has undergone a shake-up since Ullrich was linked to the Spanish blood-doping scandal. The German cyclist retired on Feb. 26.
"The team will closely monitor the progress of these investigations and develop alternatives that will provide our athletes with the best possible medical support," Stapleton said.
D'Hont was convicted of being an accomplice in the Festina team doping case in 2000.
He claims in his book that the Team Telekom riders wanted the performance-enhancing drugs, and in some cases persuaded reluctant doctors to help.
In the "mornings, the blood levels were controlled. In the evenings after the massage, new EPO dosages were given every two, three days in the hotel room," d'Hont wrote.
T-Mobile said it will continue a new program of blood and hemoglobin testing, which is performed by outside medical professionals and monitored by an independent medical review board.