Nico Rosberg has singled out Williams as a potential threat as he chases a hat-trick of Austrian Grand Prix wins this weekend.
The championship leader is not the only one expecting the Grove team to shine at the Red Bull Ring, despite the fact that Ferrari and Red Bull have been more consistent challengers to Mercedes this year.
"Traditionally, Williams are strong in Austria as they have the highest speeds on the long straight," Marc Surer, a former F1 driver turned pundit for German broadcaster Sky, said.
Rosberg had earlier told Bild newspaper: "I am especially looking at Williams. They always put us under pressure there."
However, team boss Toto Wolff thinks that Mercedes's actual challenge in Spielberg will come from the usual suspects.
"For me, the challengers are - in order - Ferrari, Red Bull, Williams and Force India," he told Italian newspaper Corriere della Sera.
However, he also insisted that Mercedes is being pushed to its limits in 2016.
Asked if F1 is witnessing the gradual end of Mercedes's era of domination, Wolff answered: "Each era always ends - even the Roman Empire experienced it."
Rosberg leads teammate Lewis Hamilton by 24 points going into this weekend's race.
