Force India deputy team principal Bob Fernley admits the Silverstone squad are "not confident" over the tyre changes made by Pirelli.
Force India were one of the few teams who adapted very well to Pirelli's aggressive tyre strategy at the start of the year as they picked up 59 points in the first eight races.
However, the Italian manufacturer introduced new Kevlar belt rear tyres at the German Grand Prix following several blowouts at Silverstone the week before.
The VJM06 didn't adapt well to the changes as both Paul di Resta and Adrian Sutil finished outside the points at the Nurburgring and Fernley feels they were "losers".
"I don't think we are confident, it's quite a significant change," Fernley said. "Obviously what we've got to look at is running it [during the Young Driver Test] at Silverstone; the good positive thing is we can do a good back-to-back comparison from only a week ago.
"The weather was quite good on race day so we've got good data to be able to do the comparisons with. But the tyre is so significantly different, and the car is designed specifically around that 2013 tyre, that we will have to re-engage design work on something that we actually thought we'd stopped because we want to move on to the 2014 car. So it's not good. It's not healthy for Force India.
"I think there are other teams as well. I'm sure Ferrari are in that situation, Lotus seemed to go well [in Germany] but it will affect them because it's quite significant again for them. And there will be more teams; there will be some winners and there will be some losers. For sure we are a loser, the question is how much do we lose."
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