Loeb, who won the WRC's season-opening Monte Carlo Rally in January, was present for a private test organised by Red Bull’s DTM partner AF Corse at Spa alongside the team’s recently-confirmed full-season drivers Felipe Fraga and Nick Cassidy.
It is understood that AF Corse was running three cars at the Belgian Grand Prix venue on Tuesday, with its regular Red Bull and AlphaTauri-liveried Ferrari 488 GT3s complemented by a third car in plain white livery.
Red Bull refused to comment on Loeb’s surprise appearance in the pre-season test, which continues on Wednesday, but also stopped short of denying the Frenchman’s presence at Spa.
Loeb has long been associated with the energy drinks giant and could be in line to replace Cassidy when the Kiwi is unavailable to race in the DTM due to clashing commitments in Formula E and the World Endurance Championship.
Cassidy is expected to miss the opening round at Portimao on 30 April-1 May as well as the Norisring races in June, with his Formula E contract with Envision taking precedence over his DTM deal with AF Corse.
The sixth round of the DTM season at Spa also falls on the same weekend as the WEC’s annual visit to Fuji in September.
Loeb, who is racing in Extreme E for Lewis Hamilton's Prodrive-run X44 team and the new FIA World Rally-Raid Championship with the Prodrive-built BRX Hunter, doesn’t face any scheduling conflicts with the DTM’s Portimao and Norisring races.
However, the Spa DTM race does overlap with the penultimate round of the Extreme E series in Chile.
The potential inclusion of Loeb would lend star power to Red Bull’s DTM line-up, especially as the Austrian brand hasn’t been able to work out a deal to place one of its Formula 1 junior drivers in the series due to multiple clashes with Formula 2 and Formula 3 calendars.
The 48-year does have pedigree in circuit racing, having finished second overall at the Le Mans 24 Hours in 2006 and scored multiple race wins in the World Touring Car Championship between 2014 and 2015.
His last season of racing in GT3 machinery, in 2013 with his own McLaren-affiliated Sebastien Loeb Racing squad, also yielded race wins in the Blancpain Sprint Series alongside Alvaro Parente.
