Toto Wolff admits he is "worried" about Valtteri Bottas’ performance slump.
Until just a few races ago, Finland’s Bottas was performing well in his first season for Mercedes alongside Lewis Hamilton.
He has been signed up for 2018.
But a few races ago, Bottas’ performance began to slump, and the problem is no better this weekend in Malaysia.
"It’s hard to say anything about it," the 28-year-old told the Finnish broadcaster C More.
One potential explanation at Sepang is a new Mercedes aerodynamic package, with only Hamilton reverting to the former specification after practice.
But Bottas said: "I don’t think that explains the big difference.
"It’s easy to say now, but if I could do it again, I would use the old aerodynamic package. But the gap in Q3 was actually huge."
His boss, Wolff, commented: "Of course I’m worried, because I want Valtteri to do well — as we all do in the team.
"In the last 3 or four races we have seen moments when he is very competitive, however, the car is quite difficult and it is not easy to find the best grip with the tyres," he told Turun Sanomat newspaper.
Wolff, however, backed Bottas to get back to his former level of performance.
"His intelligence and his skill is enough to put the puzzle together," he said.
"We still have a lot of races with Valtteri to eliminate this problem. We have very good drivers who are able to get out of difficult situations, so I have no doubt that Valtteri will be able to do that."