Two late goals ensured Bayern made it six wins out of six and extended their lead at the top of the Bundesliga table to five points, but Sammer said the performance was still not up to scratch.
"What we did today up to the 1-0 was too little," he said. "You have got to be honest about it."
The game was Bayern's eighth of the season and fifth in the last fortnight and Sammer hopes the strains of such a busy schedule were the only reasons for what he saw as a sub-standard performance.
"If it is normal for such a game to come given the rhythm, then we can take that, but if it is something mental, then we cannot accept that," he told Sky television.
"We have to evaluate the performance and not always the result."
Coach Jupp Heynckes was also unhappy about his side's performance, saying it had "tested my patience a little".
"But in the end, it was enough for a win against a strong Bremen side," he added.
"However, I had to use some clear words at half-time."