Formula 1 rookie Nicholas Latifi says Williams has not yet fully addressed the issues it faced with its 2019 car.
Williams had a positive first test with its new FW43 at Barcelona last week, completing 324 laps, although Latifi lost valuable track time with a Mercedes engine issue on Friday.
Latifi acknowledged that Williams has made a significant step since its disastrous start to the 2019 season, but cautioned that more work has to be done.
"There definitely some positive signs," he said.
"There's still some negative things with the car, some things that we still have to try and sort out, some issues - let's say characteristic - carrying over from last year, so not all the problems are solved."
Asked by Autosport about the turnaround since February 2019, Latifi agreed that Williams is in a much stronger position.
"It sounds silly to say but just the fact that everything was ready on time and waiting on the light to go out on the first day of testing was a huge psychological boost for the team, especially after what happened last year," he said.
"From my first impression of the car when I was driving on day one, I feel could for sure it's a step forward, which is great to feel as a driver because you can tell all the hard work that guys were doing over the winter, the guys and girls back in the factory, was paying off.
"How much of a step forward it is? For sure all the other teams have made a step forward, we'll find out come the first few races."
Asked to outline his goals for his rookie season, Latifi said his initial aim would be to match Russell.
"In F1 your biggest benchmark is always your team-mate because you're in the same car," he said.
"I have a very good team-mate in George, so I'm looking forward to getting to race side-by-side and go up against him and see how I can fare against him.
"So I would say the goal right now is just to get on his pace as soon as possible."
While he acknowledged Russell's suggestion that he is well prepared for a rookie, Latifi pointed out that he has less opportunity to test this year.
"I would say my overall F1 experience definitely is giving me an advantage coming in as a rookie," he said.
"At the same time I will say this is probably the most difficult year to come in as a rookie with regards to testing, two less test days, no more in-season test days, no more rookie test days.
"The track time leading up to the first few races is definitely down.
"But I feel as well prepared as I could be really, coming into my first full season."