The Italian saw his side lose 3-0 to Bournemouth in the Premier League at the weekend.
Post-game, De Zerbi said: We are having a tough season, especially in the last two or three months.
We have a lot of injuries but we have to be able to find the energy to be able to finish the season in a different way.
Motivation I think in football is 80% of our work and, in my time, we kept every game a big challenge, a big target.
In this moment, the Europa League is finished, we are too many points from the European positions in the table.
We are working for not a clear, clear target and it can happen.
It's normal but I can't accept a game without soul.
We are Brighton and we have to keep respect for ourselves, for our club, for our fans and I am sorry for that.
I am really sorry. I am suffering a lot but I am working in football for 30 years and I know this moment can happen.
We have to stop this moment quickly."