Sebastien Buemi is not ruling out a return to the F1 grid.
Since losing his Toro Rosso seat, the 28-year-old Swiss has become a top sports car and Formula E driver.
But Auto Motor und Sport said he was back at the wheel of a Red Bull F1 car last week to help Pirelli test tyres at Paul Ricard.
There are rumours Renault advisor Alain Prost is pushing hard for the works Renault team to consider Buemi for the future.