Although Williams had high hopes for the start of the season, both Maldonado and team-mate Valtteri Bottas struggled for pace in Friday practice for the Australian Grand Prix.
The Venezuelan finished down in 16th position in second practice, three seconds off the pace.
Maldonado acknowledged Williams has a lot of work to do to catch up.
"I think we are far away from the top guys today," said Maldonado. "We need to work very hard, try to understand our problems.
"The thing is they are clear - we just need to work very hard to solve it and that is it. We are a bit surprised by the performance here. But this is not the end; we need to work and that is it.
"We need to analyse why we are that slow."
When asked what was a realistic goal for the weekend, he said: "We don't know. [It's] really bad."
Maldonado said he was not sure about Williams's form after testing and reckons only Sunday's race will show the real picture.
"In the tests you never know against the others. I was never convinced and nobody is convinced until you get to race," he said.
"Even today you know more or less the other teams, what they were testing in terms of high fuel or low fuel, but it seems to be we are losing something against them and we need to see again in qualifying and try and find the problems."
He added: "I am quite comfortable in the race because we manage the tyres quite well. Not everyone managed that so we will see.
"It is not all qualifying and the pace. Remember last year's Sauber car started from 16th/17th [and scored]."
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