Berger compared it to when Daniel Ricciardo arrived at Red Bull after being promoted from Toro Rosso.
The German struggled to find his feet that season and was ultimately out-performed by the Australian.
With Leclerc’s arrival already there has been occasions where team orders have come into play from Ferrari, giving Vettel the priority, but the only time the team have contended for a win so far this season was Leclerc’s dominance in Bahrain until an engine failure.
Berger said to Italy’s La Gazzeta dello Sport: "Vettel needs to feel at home, to live in a relaxed atmosphere.
"He is suffering and cannot give 110 per cent, as happened when he was with Ricciardo when he then left Red Bull."
Despite the struggles that seem to be going on at Ferrari, Berger compared the German to that of Michael Schumacher, of which Lewis Hamilton is edging closer to match his titles haul, but also how they are different.
"Lewis has a super ego, before leaving Mercedes he wants to match Schumacher with seven titles," he added.
"He is the pilot that most reminds me of Senna.
"Seb is a hard worker like Schumacher, but compared to Michael he lacks the ability to direct the team, to ask for the hiring of key men.
"But now he is 100 per cent focused to prove that he is still the number one [at Ferrari]."