Marcus Ericsson said he was disappointed to miss out on a return to the points paying positions after he was classified in 11th place at the British Grand Prix.
Ericsson was running in the points at Silverstone but changed to Intermediate tyres early and lost track position, eventually coming home behind McLaren's Fernando Alonso.
"It is disappointing to miss out on points when we had it in the bag for quite a long time," he said.
"The first half of the race was reasonable. I had a good start, gaining some positions on lap one. My pace was good, so I was able to keep up with our direct competitors.
"It was one of those days when it was difficult to make predictions, as it started to rain on some parts of the track and others were still dry.
"It was not an easy situation, either for the drivers or for the team. Unfortunately, we made too many pit stops. We need to sit down and analayse what we could have done differently."
Team-mate Felipe Nasr did not start the race due to a gearbox problem.
"When I went out to the starting grid I got stuck in sixth gear," he said.
"As soon as I returned to the garage the team detected a mechanical issue with the gearbox. It is a shame."