Nico Hulkenberg says a lack of development in the second half of the year could leave his Renault F1 team behind Haas in the constructors' championship at the end of the year.
Renault is currently fourth in the standings but holds a slender eight-point lead over Haas in fifth place with four races remaining. At the last two races alone, Haas has outscored Renault by seven points and Hulkenberg believes the narrowing gap is a result of his team falling behind in the development race.
"It is going to be a long end to the year, especially if you don't have the sharp weapon you need to be in the fight," Hulkenberg said "So it won't be the easiest of times and quite challenging.
"I think I am pretty sure we have not made progress. The car still feels the same as like maybe 10 races ago, but have we lost performance? Have we made it worse? I don't think so. I just think that others really bolted on some good upgrades and went faster -- both on the engine and car side.
"We are just getting the cheque for it now."
Hulkenberg, who scored 52 of his 53 points in the opening 11 races of the season, said his team has been lacking a major mid-season upgrade like the one it introduced last year.
"This year we plugged along and sometimes brought little things, but never a major upgrade like last year, and those little ones even did not do the job. They were not really enough of an improvement.
"Now we are seeing and learning that we have just lost out with that approach, and we just did not find enough. It's as simple as that. Since a few weeks we are aware of this and we are reacting and trying to make it better in the future of course."