Robert Kubica in Turkey has admitted concern at the growing number of F-duct solutions within the F1 pitlane.
Kubica wary of rival F-duct
Renault is still working on the innovation, while the likes of Red Bull, Mercedes and Force India are all trialling the downforce-stalling concept on their cars this weekend.
"Some of our competitors have the F-duct now which will give them better top speed," the Pole is quoted by Germany's Auto Motor und Sport.
"In Barcelona Sauber showed how much you can get out of it when the system is working.
"We don't have it, so it may be that we will fall behind somewhat," warned Kubica.