The source, who spoke on condition of anonymity, confirmed information reported earlier by the Welt am Sonntag newspaper. The person said that first unofficial contacts have taken place in a very small group and that talks were at a very early stage.
A spokesman for Deutsche Bank and a spokeswoman for Commerzbank both declined to comment.
Speculation about a possible merger between the two banks has been rife for months, heightening under the tenure of Finance Minister Olaf Scholz, who has spoken out in favor of strong banks.
Both lenders have struggled to return to sustainable profitability since the global financial crisis.