Merson believes the Newcastle v Sunderland game will end in a draw.
Merson told the SkySports Fantasy Football Club podcast that he was impressed with how the team played against Leicester City, but they cannot afford another loss.
He believes the Spaniard will have to alter his defensive first style, with the team in need of wins to haul themselves out of the relegation zone.
Merson added that he predicts the Tyne-Wear derby will end in a draw.
He said: "Now the manager's come in, they looked a completely different outfit. They were running, working, they had more about them. I think it'll be a draw now, 1-1.
"I worry for Newcastle if they lose, the manager sets teams up not to lose, if they don't win they have to change everything about what he does, what he as a manager is about and I don't think that'll work."
What will happen if they lose, is really a consideration Newcastle will hope they will not have to address. Benitez will trust his methods for now, and with his experience in the game, he should be able to adapt to the situation required with better fortune than Merson projects.
Benitez would not have taken the job on without a plan, and even if there is a setback against Sunderland, there will still be eight games to pick up form and turn it around.