Max Verstappen and team-mate Chris Lulham and Ben Barnicoat will start only 15th for the GT World Challenge race at Portimao that Verstappen is contesting in his break between Formula 1 races.
Verstappen's return to the GT scene got off to an eventful start as he tapped Ezequiel Perez Companc's Audi into a spin in a traffic jam on his first lap in morning practice.
Stewards looked at the incident but took no action, and by the end of the second practice session the Verstappen crew was up to fourth.
But they struggled in qualifying, their Mercedes visibly running lower than most and kicking up abundant sparks in the twilight session as they managed only 15th on the 61-car grid.
While Barnicoat called 15th a "could be worse" situation, he admitted the 2 Seas Motorsport-run Verstappen team had taken a wrong turn with the set-up.
"We felt like we'd been missing a little bit of speed - we've been quite high up the timesheets but none of us were super happy," he said.
"So we tried a couple of things there and obviously it didn't quite work out - lots of sparking, a lot of bouncing in a straight line, so I think we just missed it a little bit."
The three-hour race starts at 5pm local time on Saturday. The Boutsen VDS Porsche of Dorian Boccalacci, Morris Schuring and Alessio Picariello starts from pole.