Mercedes MD Nick Fry has warned Jenson Button that there's a "clear gap" between himself and Lewis Hamilton that he needs to close very quickly.
Button made his debut for McLaren in Sunday's season opener in Bahrain, but he could only manage seventh place while Hamilton finished third.
The reigning World Champion admitted after the race that his team-mate did a "better job", but he wasn't too concerned.
"It's a fact that Lewis finished in front of me," he said. "He did a better job. I couldn't have done any more in the race," Button said.
Fry says Button has "got to work hard" if he wants to edge closer to his team-mate.
"There's clearly a gap that Jenson is going to have to close. It's absolutely self-evident," Fry told Reuters.
"I'm sure he'll be looking after this weekend at what he can do to close the gap to Lewis.
"Lewis does have 'home team advantage' at the moment but the longer Jenson stays with the team, the more that reason goes away," Fry added.
"He'll have to be looking at all the aspects of his own performance, not only how he drives but also the way he works with the team. Jenson will know all those things and he's got to work hard."
