Claire Williams has denied that the British team's youthful driver lineup could explain Martini's decision to depart as sponsor.
The alcohol brand has announced that it will stop being Williams' title sponsor at the end of the season.
The move follows rumours that the company wanted Williams to sign at least one older driver for 2018, such as Felipe Massa or Robert Kubica.
However, Williams ultimately signed 22-year-old Sergey Sirotkin to be 19-year-old Lance Stroll's teammate this year.
"We told Martini that we were looking at Sergey and they were very open to that possibility," Williams is quoted as saying by Le Journal de Montreal.
"The end of the contract has nothing to do with the age of our two race drivers.
"Martini and Williams had a successful cooperation and they achieved their goals. They're not only leaving Williams but also Formula 1 as a whole."
Martini's departure will nonetheless leave a hole in the team's budget for 2019, although Williams played down the impact.
"As an independent team, we have an active commercial department that is always looking for new partners," she said.
"I don't want to say now that we're looking for a title sponsor, because we're looking for a budget to go racing. Let's see how the situation develops this year."
The new season gets underway with the Australian Grand Prix on March 25.
