TV pictures clearly showed the Senegal star spitting at Celtic fans towards the end of the 1-1 draw at Celtic Park.
Liverpool say they will talk to Celtic so that the money can be given to a charity of the Scottish club's choice.
Diouf is also being investigated by police in Scotland.
The incident happened when the player fell into the crowd with full-time approaching, and as he climbed to his feet a couple of fans touched his head.
"The boy has made a mistake. He knows that. We all make mistakes in life because we are all human," said Houllier.
It's the second time this season Diouf has been involved in something like this.
In November, he was accused by West Ham fans at Anfield of spitting at them.
Then police investigated and took no action.