Researchers from Britain's University of Kent used methods from conservation science to estimate that COVID-19 could have emerged in China as early as October 2019.
That's two months before the first case was identified in the central city of Wuhan.
The new study released Friday (June 25) estimates the virus had probably already spread globally by January 2020.
China's first official COVID-19 case was in December 2019 and was linked to Wuhan's Huanan seafood market.
However, some early cases had no known connection with Huanan, implying that COVID-19 was already circulating before it reached the market.
A joint study published by China and the World Health Organization at the end of March acknowledged there could have been sporadic human infections before the Wuhan outbreak.
Leading scientists continue to say that a lab leak can't be ruled out.
Jesse Bloom of the Fred Hutchinson Cancer Research Center in Seattle recovered deleted sequencing data from early COVID-19 cases in China.
The data showed that samples taken from the Huanan market were "not representative" of the virus as a whole and were a variant of a progenitor sequence circulating earlier.
Critics said the deletion was further evidence that China was trying to cover up the origins of the virus.
Another study by Australian scientists published on Thursday (June 24) found evidence that suggested COVID-19 was already adapted to humans when it first emerged.
It said it was possible there was another unidentified animal that served as an intermediary species, but the hypothesis that it leaked from the lab could not be ruled out.