The head coach told the Packers' website: "I told them we missed an opportunity. I talked about our performance lacking the necessary details to be successful. It goes back to the fundamentals, whether it's tackling or run blocking.
"We started very well on defense, but we did not start well on offense and special teams too often put us in bad field position.
"We definitely played with an edge. We had issues with the details and mental aspect of the game. Our problems in those areas led to the inconsistencies in our performance. We need to clean those areas up this week, and we have to be much better than we were in San Francisco."
The Packers play the Washington Redskins in their next game on Sunday.