Valtteri Bottas has admitted that Williams are struggling to match the pace of the resurgent Ferrari.
The Oxfordshire-based outfit finished behind Mercedes and Red Bull in the 2014 Constructors' Championship and were predicted by many observers to be the team most likely to carry the challenge to the Silver Arrows this season.
However, Sebastian Vettel's Malaysian Grand Prix victory for Ferrari has altered that perception and Bottas believes that Williams have plenty of work to do to catch up.
He told Autosport: "We maximised the result but we are missing race pace - and quite a big amount.
"With the ideal race, starting at the front, the gap wouldn't be that big but it is too big, much bigger than we expected.
"It shows we have a lot of work to do. There is a lot more potential, we just need to get more performance because it is possible others made huge steps."
Bottas finished fourth in the 2014 drivers' championship.
