The German publications Bild and Sport Bild might have discovered the reason.
In the Bahrain paddock, correspondents Bianca Garloff, Ralf Bach and Nicola Pohl noticed that when wearing casual clothes, Rosberg is sliding his left foot only partially into his shoe.
"I hurt my toe while jogging on the beach," he told Bild. Sport Bild reports that the injury was sustained last week, when the 28-year-old was holidaying in Dubai.
Rosberg confirmed that he brakes with his left foot but played down the impact of the injury on his driving.