Diouf and Diao, who cost Houllier a combined fee of £14.7m, failed to impress the Frenchman with the excuse that they had been obliged to attend an official function in their homeland before jetting back to Liverpool.
Houllier said: I am not happy and will let them know. They should have been back on Monday - and I am not pleased.
"They said they had to go back to Senegal but I told them we had a game on Wednesday.
"I am not sure who is to blame but I don't want an explanation and it will be dealt with internally.
"If the game is played in the same continent, such as England next week, players have to be back at their club within 24 hours.
"When it is in a different one, they have 48 hours and I can tell you it does not take that long to come back from Tunis.
"They are not in the squad for Portsmouth - no chance. I will tell them I am not happy and I know that some Senegal players went back earlier."