"We have agreed on a joint architecture for a sports car. What is important is that there will be two different vehicles that are authentic to the two brands," Frankfurter Allgemeine Zeitung on Monday quoted Diess as saying.
BMW and Toyota had in January signed an agreement to cooperate on various areas including lithium-air batteries and lightweight technology.
They also said at the time they would study the potential for a joint platform for a mid-sized sports vehicle in a feasibility study to be completed by the end of 2013.
Frankfurter Allgemeine said that Diess declined to provide details on the models that would result from the cooperation.
Reporting by Maria Sheahan; Editing by John Stonestreet