Nico Rosberg beat Lewis Hamilton by five points to win the F1 World Drivers’ Championship last year but retired days later.
The 31-year-old’s shock move has left Mercedes scrambling for a new driver with director Niki Lauda keen to get a deal done before the beginning of 2017.
Lewis Hamilton will be unbeatable next year
But reported efforts to lure Valtteri Bottas away from Williams have failed so far and while McLaren’s Fernando Alonso has ruled out switching teams for next season
But Ecclestone is worried that unless Mercedes recruit the best around - such as Red Bull’s teenage sensation Max Verstappen - the 2017 F1 season will be a race for second place.
"I don't think anybody is going to beat Lewis,” Ecclestone told Sky Sports.
"Verstappen has been super.
“When I say nobody, maybe Max in that car could hurry Lewis along a little bit.
"I think nobody would want to buy tickets and go to watch a race or watch on television Lewis disappearing from us when the lights go off and probably lapping the field a couple of times.
"It would be bad for everybody and bad for Lewis as well, because I think he wants to win fair and wants to beat somebody.
"The problem is a simple one: the Mercedes team, engine, everything, is perfect and they've got the best driver in the world.
"I hope I'm completely wrong in my assessment of the championship with Lewis.
“I hope I am wrong and whoever goes and sits in the same team can beat him or hurry him up that he makes mistakes.
"My personal opinion is that it's not going to happen."