Grosjean was confident that the issue had been solved after struggling home 10th in Australia, over 90 seconds adrift of victorious team-mate Kimi Raikkonen.
But during Friday practice the car problems returned, with the car behaving erratically and variously giving him understeer and oversteer.
Asked by AUTOSPORT if he feared a repeat of his Melbourne difficulties, Grosjean replied: "A little bit. We still have problems with the car, the same as we had in Melbourne and we don't understand it.
"Suddenly, it [the car] can bring you different things [handling characteristics] and it doesn't make the car easy to drive.
"But the team is going to work hard and if we can change a few pieces to make it consistent, then we will do it for tomorrow.
"I keep my fingers crossed we will solve the issue."
Grosjean confirmed that, aside from the modified exhaust package run by Raikkonen, the specification of his Lotus E21 is identical.
But he doesn't think that a chassis problem or undetected damage is the root of his struggles.
"It hasn't got any damage but what we see from P1 to P2, without changing much, the car has changed," he said.
Grosjean added that he was upbeat about the development path being taken by Lotus.
Despite not running the new package, he is confident that it is a step in the right direction.
"It looks a good point for the future," he said. "Unfortunately I will now have it this weekend."
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