The 23-year-old has joined the German team from Williams ahead of the 2022 season, replacing Valtteri Bottas.
Russell is yet to take a Grand Prix win, and has just one podium in Formula 1.
Marko, head of Red Bull’s driver development program, challenged Russell to live up to the confidence shown in him by Mercedes.
“Let’s see what Mr Russell will do at Mercedes and whether the praise he has received in advance is justified,” remarked Marko to Austrian outlet Autorevue. “I want to see that first.
“There’s no discussion in qualifying, he’s sensational there but if you look at his race speed, he wasn’t far ahead of [then Williams team-mate Nicholas] Latifi.”
Russell’s likely 2022 teammate Lewis Hamilton is yet to confirm that he will return to F1 next season.
The seven-time world champion was left “disillusioned” by the contentious ending to the Abu Dhabi Grand Prix, when Max Verstappen was able to snatch both Grand Prix and Drivers’ Championship victory.
Russell previously filled in for Hamilton, who had tested positive for Covid-19, at the 2020 Sakhir Grand Prix, finishing ninth in the Mercedes.