Felipe Nasr admits it is frustrating to watch Sauber's rivals make progress while the team waits to bring significant upgrades to its car.
Sauber started the season with a strong result in Australia, where Nasr finished fifth on debut, but has since slipped down the pecking order as other teams have made gains. Nasr says Sauber's current car is more or less the same as the one it raced in Australia.
"I just feel our car hasn't been updated at all," Nasr said. "We have had minor updates on set-up and suspension, but the bigger lap time is to come on the aero side. The car gets more stable, you are able to brake later, you carry more speed into the corners and you make your tyres work for longer.
"I am sure once you have this fundamental of the car working better, it improves the other areas. We need to have a bit of patience for the work on the key areas but the main deficit of the car is the high-speed corners."
Sauber is due to introduce a significant aerodynamic upgrade and Ferrari power unit in Belgium and Nasr is convinced the team would have been in a good position if it could have brought new parts sooner.
"It could have been pretty good. We could have been fighting with those top ten positions most of the time. If you look at the steps made by Force India and Lotus over the last races it's enough to have put them back in the points.
"In the first four races we were fighting for those points and now we are a bit far from them, but that's what we face. It's difficult, not only for me but for the team as well, to accept that but it's not only the matter of bringing something new if you don't know it's going to work."
Sauber recently appointed Mark Smith, who formerly worked for Jordan, Red Bull, Force India and Caterham, as its first technical director since 2012. Nasr welcomed the move and thinks it should help Sauber focus on making the progress it needs to.
"100%," he said when asked whether Smith's appointment was what Sauber needed. "In China we brought a new front wing and it was not what we expected. So bringing in a new technical director for the team to direction the team and give a good overview of where the car is at the moment and where we need to work on the short-term, the medium-term and the long-term.
"The basic of the car is quite good but to make a step forward - and I don't mean one or two tenths, we are thinking to make something bigger - when the team spends money on the right things you expect a bigger jump, you are not trying to find on a front wing just find half a tenth. I think it was a smart move from the team and we need to give time for these things to work.