Jenson Button said he had struggled with his McLaren around the Sepang circuit throughout the first day of practice and has yet to get the car to his liking.
Five days on from his win in Australia, the reigning World Champion was third and fourth fastest in the first two sessions in Malaysia, but admits he has found it tough so far.
"I'm getting there slowly, but it's been a long afternoon," said Button. "I haven't really come to grips with the car around here, I really struggled with the balance and I haven't found something I like.
"Very twitchy rear end and I just can't deal with it at the moment so we've been working with that. Eventually, toward the end of practice, I started feeling better but there's still a long way to go before I'm happy, so it will be a long night tonight."
Several drivers complained of difficulty finding a balance with the softer tire in practice today. Button reported over the radio during the session that he was struggling with both understeer and an unstable rear.