Mark Schmidt is at the center of the comprehensive doping investigation, which includes 23 cyclists and skiers from eight countries.
According to the German news site focus.de, Schmidt admits that from 2012 he has mainly helped cycling and winter athletes to dope themselves.
However, according to the statement read out by his lawyer, the doctor emphasized that it was not about money.
"I have not made any profit from doping," he says.
He also opposes the accusation that he would have put the athletes in danger.
"It was always important to me that the health of the athletes was not harmed."
The Munich prosecutor's office accuses the 42-year-old doctor of almost 150 crimes - and Schmidt pleads guilty to most of them.
The scandal erupted during the World Ski Championships in Seefeld 2019 when Max Hauke was caught with a syringe in his arm.
However, the investigation had been launched earlier, following a documentary by German ARD and statements by the Austrian cross-country skier Johannes Dürr who admitted that he had been doped.
Another four people are accused of having helped the doctor to collect blood, among other things.
Mark Schmidt risks up to ten years in prison, according to Reuters.
A verdict is expected just before Christmas.