Red Bull team principal Christian Horner says the team are looking into why Daniel Ricciardo was so off the pace in the Japanese GP.
Ricciardo began the race from fourth on the grid but struggled in Suzuka and ended up down in sixth place, with team-mate Max Verstappen instead impressing as he finished second behind Nico Rosberg.
Ricciardo was expected to be much quicker in Japan and Horner says the team are investigating the problems he encountered as he admitted he had engine issues which hampered him.
"Daniel has looked a little bit down on straight line speed, and the engine guys are having a look at that," Horner said.
"The engines are towards the end of their life now. Plus his car was perhaps touching a little bit [on the floor] down the straight too, but I am sure there will be a lot of investigation from the engine guys into that."