Christian Horner will be stunned if Sebastian Vettel turns his back on Ferrari at the end of the season - but the Red Bull team principal believes Lewis Hamilton's Mercedes team are working to sign his title rival.
Vettel, who heads Hamilton by 20 points in the championship ahead of this weekend's British Grand Prix, is in the final campaign of his three-year deal with Ferrari.
It was revealed on the eve of Hamilton's home race that Mercedes boss Toto Wolff attended Vettel's 30th birthday celebrations in Switzerland earlier this month.
And Horner, who oversaw Vettel's four consecutive championship triumphs at Red Bull, suggested that Wolff may have urged the German to remain free for 2019 - the season after Hamilton's three-year deal with Mercedes expires.
"I'd be amazed if Seb left Ferrari," Horner said. "I would think he's got Toto in his ear trying to say extend for a year. He's probably got Ferrari saying it's three years or nothing.
"I guess he wants to see through what he started at Ferrari. He went there for a reason, to build something and very much emulate what Michael Schumacher had done. Stepping out now with the progress they have would be a job half done."
Vettel faced an investigation from the FIA, Formula One's governing body, earlier this month after he deliberately drove into Hamilton at the Azerbaijan Grand Prix.
The German, who escaped any further action, was accused of setting a bad example to the sport's young fans, not least by Hamilton who described his actions as a "disgrace".
Vettel later apologised to both the FIA and Hamilton - but Horner believes his former driver, who idolised his compatriot Schumacher as a child, has adopted his hero's win-at-all costs mentality.
No driver in the sport's history has won more titles, races, or indeed claimed a greater number of pole positions than Schumacher, but the seven-time champion's career was marked by a number of misdemeanours.
"Sebastian's got this huge desire within him, and the records mean a lot," Horner said. "Michael was very much his idol and I think what we see sometimes is that killer instinct of 'I want to win', sometimes at all costs.
"He comes across as spoiled but I think you've got to put yourself in his scenario and his shoes. He's lifted Ferrari from where it was to where it is now, he's been a big driver in that.
"Sebastian wears his heart on his sleeve and he is involved in a very intense title battle. He sees an opportunity to be a champion again this year and he knows he's going to need everything going his way against Mercedes to achieve that.
"He has zero filter between what he thinks and what he says sometimes or what he does and that's the great side of him, but sometimes it gets him in hot water as well."