The deal could result in Telefonica's Endemol working with RTL's Pearson Television operation, which is itself soon to be rebranded.
The possibility of a merger between RTL and Telefonica Media is also being mooted, however nothing has been confirmed so far.
RTL is Europe's largest free-to-air broadcaster with free TV channels in Germany; France; the UK, where it owns Channel 5; and Benelux.
A deal would give it access to Endemol's popular programming including Big Brother, which was successful in eight European countries.