Fernando Alonso has described McLaren's power deficit from their Honda engines during the Brazilian GP as "amazing".
Alonso was frustrated in his race-long battle to pass Felipe Massa at Interlagos for seventh place, spending the entire race tucked up behind the Brazilian's Williams but unable to pass his Mercedes-powered rival due to the lack of straightline speed from McLaren's Honda engines.
Alonso and team-mate Stoffel Vandoorne were slowest of all through the speed traps in qualifying.
"We had a fantastic car but we cannot overtake," Alonso told Sky F1. "The lack of power was amazing. Even with DRS, Felipe was still pulling away."
Vettel wins despite Hamilton charge
WATCH: Mayhem on the first lap
Massa: Brazil farewell like a victory
McLaren and Toro Rosso will effectively swap engines in 2018, with McLaren taking on Renault power, and Alonso warned: "The lack of power will be quite worrying for Toro Rosso."
The Spaniard added: "For us it is a happy weekend but the lack of speed was alarming. Mexico and here we have been super-slow on the straights."
Renault have had plenty of engine issues of their own in recent weeks and both Red Bull cars had to run at reduced power in Brazil to reach the chequered flag.
But Alonso shrugged off those concerns.
"Renault is the best engine company in the past 15 or 20 years if you see all the world championships so l don't think we should be too worried," he said.
Courtesy of his eighth-place in Brazil, Alonso now heads McLaren team-mate in the Drivers' Championship by two points ahead of the season finale in Abu Dhabi.
Don't miss the F1 Report on Wednesday at 8.30pm on Sky F1 as Williams co-founder Sir Patrick Head joins Marc Priestley and Natalie Pinkham to review the Brazilian GP.
Comment below to get involved in the debate, but please adhere to our House Rules. If you wish to report any comment, simply click on the down arrow next to the offending comment and click 'Report'.