Both drivers offered robust endorsements of Vasseur ahead of this weekend's Bahrain Grand Prix, hosted in Malaysia's Sepang this year, with Leclerc describing the team boss as "extremely valuable" and Hamilton giving him his "full backing."
Ferrari had moved to shut down speculation by reiterating its "full confidence" in Vasseur, even as reports gathered pace after Horner said the Italian outfit was the only team he would consider joining without an ownership stake.
"I've always said how much I trust Fred and how important he is for the team. We have a very special relationship," Leclerc told reporters as he dismissed what he described as "silly rumours" in the paddock.
"But over that, I think he's extremely capable in what he does and I think he's been extremely valuable so far. He will be extremely valuable in the years to come as well."
"To manage people, which is exactly where you've got to be good at when you are a team principal, he knows what the words are to be used and what the conditions that someone needs to be put into in order to extract the maximum out of an individual."
Formula 1 veteran Hamilton was equally supportive when asked about the team structure.
"Fred is a fantastic leader. He really is the guy to take this team in the right direction," the seven-time world champion said.
"He's helped us get to the second in the constructors' championship. That's a huge step from last year."
Mercedes leads the constructors' standings, where Ferrari finished fourth last year.
The show of unity comes as Ferrari faces performance challenges, with both drivers acknowledging a power deficit compared to their rivals and Hamilton being frank about the team's struggles.
"The deficit we have is simply just on engine and that's something we don't shy away from," Hamilton said. "We know that every weekend we carry a four-tenths deficit, if not sometimes six-tenths, just in straight-line power.
"We're aware of it, and that's something we need to try and work on, and they're working extremely hard to try and fix that for next year."
Leclerc said Ferrari's deficit went beyond engine power.
"Sure, we have a power deficit compared to our competitors, but it doesn't only come down to that," he explained.
"In terms of chassis and aero as well, the others are catching up and have brought significant upgrades recently, which makes them very strong in the corners. We need to improve on every front."