Vettel insisted earlier this week that he does not have the power to prevent championship rival Hamilton from moving to Ferrari, and insisted he would welcome his arrival.
Although Mercedes are confident Hamilton will stay, the Brit’s future remains in some doubt following his failure to extend his contract which expires at the end of the year.
Webber’s relationship with Vettel descended into turmoil during their five years together at Red Bull in which the Australian was beaten by his team-mate to four consecutive titles.
Webber claimed Vettel was afforded preferential treatment by Red Bull’s bosses, and although he has now patched up his relationship with the Ferrari driver, Webber rebuffed Vettel’s claim that he would be keen to team up with Hamilton.
“He would block it,” Webber told Press Association Sport. “If Bernie Ecclestone was still in charge of F1, he would have Sebastian and Lewis at Ferrari next year. He would make that happen.
“Ferrari is an option, and an interesting one for Lewis, but he needs to capitalise on the momentum he has at Mercedes.
“Ferrari have not won a world championship since 2007 and that is a long time and something that Lewis must take into consideration.
“He can have the sexy factor of joining Ferrari but he has got to have the trophy cabinet, too, and he is a guy that demands trophies.”
Hamilton, 33, and Mercedes claimed at their Silverstone car launch back in February that his contract extension was likely to be rubber-stamped before the season-opening race in Melbourne.
But more than three months later, they appear no closer to striking an announcement – with the driver stating ahead of Sunday’s Monaco Grand Prix that he is not in a rush to get the deal over the line.
Mercedes boss Toto Wolff emphasised on Thursday that he is entirely confident Hamilton will extend his stay.
Rival boss Christian Horner, however, claimed the deal was being held up due to the “grotesque” amount of money involved. It is estimated Hamilton could earn up to £40million-a-year.
“Lewis is in charge of the contract,” Webber, a two-time winner here in Monaco, added. “He is the athlete and the guy who pulls the strings for his own motivation and his own demands as to what he enjoys from the sport.
“Is he enjoying it? That is a question for him, and whether he wants to continue racing or change teams.
“He is in tremendous shape, driving incredibly well – as we saw with his win last time out in Barcelona – and he has got the team around him. I would love for him to continue racing in the environment he is in.”
Daniel Ricciardo topped the times ahead of his Red Bull team-mate Max Verstappen in Thursday’s opening free practice for this weekend’s Monaco Grand Prix.
The big-smiling Australian clocked a best lap of one minute and 12.126 seconds to outpace the young Dutchman by one-tenth of a second.
Championship leader and defending four-time champion Briton Lewis Hamilton was third for Mercedes, three-tenths adrift of the quickest time, ahead of title rival and fellow four time champion German Sebastian Vettel of Ferrari.
Finn Kimi Raikkonen was fifth in the second Ferrari ahead of Spaniard Carlos Sainz of Renault and Finn Valtteri Bottas who was seventh in second Mercedes.
Mexican Sergio Perez was ninth for Force India ahead of a controlled Frenchman Romain Grosjean of Haas and Russian rookie Sergey Sirotkin of Williams, who bounced back from an early skirmish.
On a bright clear blue-skied morning in the Mediterranean principality, Mercedes were quickly into their stride with both men topping the times in the opening minutes before Red Bull joined the fray in earnest.
Thereafter it was cut and thrust between the two teams in a session of few incidents – Sirotkin clipping the barriers and damaging the right rear wheel of his Williams and Fernando Alonso being sidelined for repairs to a braking issue.
The Spaniard returned to wind up 17th.
As many expected, including Hamilton, the Red Bull drivers revelled in the handling of their car on the tight and unforgiving street track as both Verstappen and Ricciardo topped the times using the new ‘hyper-soft’ tyres on the resurfaced track.
Valtteri Bottas is celebrating the 20th anniversary of fellow-Finn Mika Hakkinen’s sole Monaco victory by wearing a helmet in the design and colours used by the double Formula 1 champion.
In a move that maintains a tradition for tribute helmets at the Monaco Grand Prix, Bottas has adopted Hakkinen’s three blue stripes on a white foundation.
“He won here 20 years ago and that year he also won the title,” said Bottas. “I wanted to pay a tribute. I respect him as a driver, as a guy, and I always loved the paint as well.”
Other drivers including Belgian Stoffel Vandoorne, Monegasque Charles Leclerc and New Zealander Brendon Hartley have revealed special crash helmets featuring a Monaco theme.
Bottas also responded to Mercedes team-mate Lewis Hamilton’s remarks suggesting a laid-back attitude to a new contract.
“There isn’t any sticking point. There just hasn’t been any rush,” Hamilton said earlier.
“There’s no discussion with anybody else, there’s no consideration for anybody else, it’s just (me) taking my time.”
To which Bottas, who has a one-year contract with Mercedes, responded by saying he hoped both would be with the team next year.
“First of all, I would like to stay here,” said the Finn. “That is my goal for the long term. It would be nice if Lewis wants to stay and finds an agreement.
“I enjoy working with him, I enjoy the challenge he gives me. I enjoy the fact he’s a four-time world champion and at the moment I’m none. It makes me try harder to be better.
“It wouldn’t change my mind that I want to stay here, but I think we work well together.”