The youngster stepped in for Hamilton, who had contracted coronavirus, and would have won the race but for a horrific late pit stop and tyre puncture.
“When he drove the Mercedes last year, that catapulted his self-confidence up even more,” Capito added.
“He is a very open guy and a demanding driver for the team.
“He’s a true professional, which is rarely seen at his age. I am sure he will become champion one day.”
Meanwhile, Mercedes chief Toto Wolff explained why picked Russell to replace Hamilton in Bahrain.