"It's unforgivable that I got behind the wheel under the influence of alcohol,” he said in a statement on Wednesday. “It’s a huge mistake which I regret deeply.”
Police described the collision as a drink driving incident causing tens of thousands of francs worth of damage, but did not identify Ullrich as the driver at fault.
But the 40-year-old former Tour de France winner, who lives in Switzerland, admitted his involvement in an interview with Swiss tabloid Blick published on Wednesday.
The newspaper said the German’s silver Audi A6 station wagon rear-ended a Citröen C3 Pluriel at a stop sign near the village of Happerswil in the Swiss canton of Thurgau on Monday, shortly after 8pm.
The Citröen flipped over from the force of collision, while the Audi slammed into a Alfa Romeo 147 before ending up in a field, according to the report.
“I’m sorry,” Ullrich is quoted as telling Blick. “I was stressed, coming from an appointment, and wanted to go home as soon as possible.”
Ullrich told the paper that he was driving by his own estimate 20 kilometres an hour too fast.
“My God,” he said, “that can happen to anyone.” He initially told the paper no alcohol was involved.
However, Thurgau cantonal police said on Tuesday that the accident was alcohol-related.
Police said they obtained a 1.4 blood-alcohol reading from the driver - almost three times higher than the legal limit of 0.5. They added the accident was caused by the driver not braking in time.
Ullrich’s accident is the latest chapter in a story of an athlete whose successful career was tarnished by doping offences.
He went on to capture gold and silver medals in the Sydney 2000 Olympics after winning the Tour de France in 1997.
But in 2006 he was barred from the classic French race amid doping speculation and he retired the following year.
The Lausanne-based Court of Arbitration for Sport found him guilty in 2012 of a doping offence and he was stripped of all results obtained since 2005.
Last year, Ullrich admitted to blood doping with the help of Spanish doctor Euefemio Fuentes.
This week's accident is not the first time the cyclist has been implicated in a motor vehicle accident.
In 2002, his driver's licence was suspended after he was caught drink driving in Germany, crashing his Porsche into a bike rack.
SEE ALSO: Star cyclist Ullrich guilty of doping