Four-time World Touring Car champion Yvan Muller has tested one of Volvo's S60 Polestar cars at the Portimao circuit.
Muller, who called time on his 11-season stint as a driver in the championship at the end of 2016, was seen testing at the Algarve venue with the Polestar team in one of its TC1 cars, as revealed by Autosport's sister brand Motorsport.com France.
Volvo will expand its set-up to run three cars in the WTCC this year, having last season run Thed Bjork and rotated Fredrik Ekblom, Robert Dahlgren and Nestor Girolami in its second seat, but is yet to announce any of its 2017 drivers so far.
Dahlgren had been a leading contenders for one of those drives, but confirmed last week that he had parted company with the manufacturer.
Polestar Cyan Racing said it would not comment on private tests, and that it would be announcing its driver line-up later this month.
Additional reporting by Emmanuel Rolland