But Osterreich newspaper reports that in the last days, he has made his single seater debut with a day of 'secret testing' in a Formula 4 car at Valencia.
"Mick is certainly talented," team boss Peter Mucke said, "but you cannot say absolutely that a good kart driver will be fast in a formula one car."
He added: "It is no good only having a great name as a driver, you have to be fast. After a day of testing, no assessment of Mick is possible yet."
Osterreich suggested that this week's F4 test was actually a prelude to a possible single seater debut for Mick jr in 2016, following another season of karting.
Manager Sabine Kehm said: "I don't want to say anything."