Red Bull duo Sebastian Vettel and Daniel Ricciardo believe that the reigning world champions could be set for a struggle at this weekend's Russian Grand Prix.
The duo spent much of Friday's practice sessions at Sochi Autodrom outside of the top 10, with Vettel's hot lap on Option tyres earning him ninth place overall, albeit almost two seconds behind Mercedes driver Lewis Hamilton.
"It looks like we will struggle here," conceded Vettel.
"It’s a nice track, but maybe not made for us."
Ricciardo ended the day in 13th position having stopped on track during the final 10 minutes of the session due to a Power Unit issue.
"It was our last Friday with that engine, so it’s not a worry that she turned off at the end there," he said.
"We tried a few settings and we’re not so fast here, the straights are long and we’re suffering a bit."