Dr Helmut Marko says he hopes Aston Martin treats Sebastian Vettel fairly in 2021.
Vettel entered F1 as one of Marko's Red Bull juniors and went on to win four world championships, but his subsequent Ferrari career is now ending in tatters.
"He makes an unusual number of mistakes time and time again," Marko told Sky Deutschland.
"You can't deny it. He's two or three tenths on average away from Leclerc."
Racing Point, to become Aston Martin next year, is hopeful leaving the Ferrari atmosphere will trigger a return of the 'old Vettel' next year.
Marko agrees: "Sebastian is a sensitive person, and although he has been in Formula 1 a long time, this separation was very difficult for him. This is not the Vettel we know from our time.
"What we see is nowhere near the Sebastian who won four titles," he added.
Marko thinks the internal politics at Ferrari - with Charles Leclerc backed by Nicolas Todt, the son of FIA president Jean Todt - also hurt Vettel.
"He's never had a situation like this, and the spiral now is downwards. Sometimes he even makes rookie mistakes that certainly come from the psychological side," Marko said.
"It shows how important a cool head and strong mental position is in racing. At the moment it doesn't work for him at all."
But Marko is also worried that Vettel could also come unstuck at Aston Martin, even though that team is promising to rally around the 33-year-old German.
Marko said of Vettel's 2021 Aston Martin car: "It will definitely be a competitive package.
"But when you hear that all the updates already go to Stroll junior and only when there are three copies does Perez get them, I hope that they treat him (Vettel) fairly," he added.
Marko agrees that Vettel is good for Aston Martin's image, "but it is even better for Lance Stroll's image for him to beat a four-time world champion".