Sebastian Vettel would stop Lewis Hamilton from joining him at Ferrari, his former teammate Mark Webber has claimed.
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 teammate 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.
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"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 40 million pounds 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."
