That is despite the fact that, on Monday, McLaren wished its "McLaren Young Driver" de Vries a happy 22nd birthday on Twitter.
But RTL cited "sources" as it claimed that de Vries, whose GP3 teammates Charles Leclerc and Alexander Albon finished 1-2 in the 2016 season, is in fact leaving the McLaren programme.
"He will test a Ferrari GT car next week," the broadcaster declared, explaining that de Vries is in the running for a full-time world endurance championship seat.
After finishing just 6th in the 2016 GP3 championship, de Vries "has not found a seat" in the F1 feeder series and lost McLaren's backing, RTL GP added.
McLaren has been contacted for comment.