Toto Wolff has moved to play down suggestions that Daniel Ricciardo might be at the front of the queue to join Mercedes next year.
Red Bull driver Ricciardo is on the market and linked with potential moves to either Mercedes or Ferrari.
That is despite the fact that negotiations over a new contract with Hamilton have reportedly stalled.
Wolff said: "At the moment we are not looking at drivers outside of Mercedes.
"First of all, we support our two guys. That is the priority. If you're happy with your wife, you don't look at other women."
Wolff suggested that if Mercedes does need to make changes for 2019, the replacement will be picked from the Mercedes pool.
"We are very happy with how Valtteri has been driving and we do not need to talk about Lewis -- I think he's the best driver today," he said.
"Then there are the young guys with us like Esteban Ocon and George [Russell]. I'm optimistic about the future of Mercedes."
Wolff said that the driver topic for 2019 is not an issue for now anyway.
"We need a few more races, get into the European season and then go to Canada and it's an intense July after that," he said. "After that I'll have a better perspective."
The 2018 season continues in Spain this weekend.