Sebastian Vettel's former boss has suggested that the German driver may soon run out of patience for Ferrari.
Christian Horner, who oversaw Vettel's four consecutive world championships for Red Bull, told Sport Bild that he senses a lack of calm in the 29-year-old's current disposition.
"I have the feeling that Seb is a bit rattled," Red Bull team boss Horner told the German newspaper.
"I know from personal experience that he has to feel good in order to perform well. And I'm not sure whether he likes [Ferrari president] Sergio Marchionne's pressure.
"I can well imagine that in 2018 Seb will switch to Mercedes if he doesn't start making progress with Ferrari."
The Italian press is currently characterising Ferrari as being in 'crisis', having failed to capitalise on its progress and being out-performed in recent races by Red Bull.
