So far, the relationship between the silver-clad pair has been amiable, but a growing tension was noticeable immediately after Sunday's Spanish grand prix.
It was there that Hamilton finally took the championship lead from his German rival, after defeating Rosberg for the fourth consecutive race.
"Formula one is always full of surprises," he told APA news agency.
"But as it looks today, I can hardly imagine that it will not keep going like this," added Berger, referring to Brackley based Mercedes' utter dominance so far this season.
And as the internal fight gets tougher, so too will Mercedes' role in managing the bickering pair, Berger explained.
"It's still early, with everyone getting on well," he said. "But I don't think it will be long before Rosberg and Hamilton clash."
Berger said one problem could be Rosberg, realising the need to revert to psychological means to unsettle Hamilton.
"Hamilton is maybe the fastest in the field, but he's very emotional," he said. "I think it is possible to put him out of balance.
"Rosberg knows that he must be clever to compensate for the slight advantage Hamilton has with natural speed.
"(Mercedes chairman) Niki Lauda will have his hands full soon," he said, perhaps referring to the triple world champion's insistence that team orders will not be imposed between Hamilton and Rosberg.
"I have already told him (Lauda) that he will be like a nanny this year," smiled Berger, a former Toro Rosso co-owner and once BMW's motor sport director.
54-year-old Berger also warned Hamilton not to expect his dominance to go unrivalled by Rosberg in 2014, despite the Briton's run of dominance recently.
"I am sure that with his (Rosberg's) determination and perseverance, he will make Hamilton's life difficult," he said.
Meanwhile, Berger rubbished criticism of this year's new-look F1, including his old friend Dietrich Mateschitz's claim this week that drivers are nursing cars to the chequered flag because they are conserving fuel.
"Nonsense," he insisted. "Just look at Hamilton and Rosberg, driving every lap on the limit."
However, he said he understands reigning world champion Red Bull's frustration.
"The truth is, Mercedes is where they are because they did a very good job. Red Bull did as well, but Renault not as much, so this (criticism) is almost pure frustration."