Milan meet Lazio after last weekend's defeat at Parma.
Fonseca said: "We are aware that we have not started well, but there is one very positive thing: we are all in agreement, we are united.
"We want to look for solutions and that is what we have done this week. It is easier to work when we are all together. We have had a good week of work. I think we have understood what is really important to improve. We are united, we have worked well, I expect to see a different Milan tomorrow.
"We talked after the game: we all think the same. We were a bit sad the first day after Parma, then we reacted and it was a very positive week. I don't like depression or looking for excuses: I'm here to look for solutions. Let's see if tomorrow was the right path."