Daniel Ricciardo must decide whether his future is at Red Bull by August or the team will look elsewhere, boss Christian Horner warned.
The Australian is in the final year of his contract and has been linked with a move to Mercedes or Ferrari.
But Red Bull are only willing to wait so long for a decision from Ricciardo, who has made a solid start to the 2018 Formula One season and won the Chinese Grand Prix earlier this month.
Horner said the team wanted a decision from the 28-year-old no later than the season break in late July and August.
"There should be a decision by the summer break at the latest," he told Auto motor und sport.
"We do not want to wait forever. We have other good options. Our priority is to continue working with Daniel.
"If that does not work, we'll pull the other options."
Horner said Renault driver Carlos Sainz Jr., 23, was an option for Red Bull if needed.
"The most obvious is Carlos Sainz. He is under contract with us," he said. "And then there are a few young drivers."