Houllier said: "They will all make a much bigger impact next season and really come good. Diao and Diouf came straight after the World Cup. Maybe it was my fault because I should have taken into consideration the fact that they'd also played an African Nations Cup as well in February.
"It's just like asking Michael Owen and Steven Gerrard to have played the European Championships in February, taking a month of their energy and all the extra games and getting right to the final - like Senegal did in the African tournament and then in June playing the World Cup.
"Everybody here would have gone berserk at such a workload and asked 'what's going on here.' Maybe I didn't pay much attention to the fact that they could well have been a bit tired.
"I'm very pleased with Diouf. He's 22, has skill and has come to terms with our game towards the end of the season. I'm sure he'll be better next season.
"He can bring some spark to a game. Diao is different. We took him because we weren't sure of Steven Gerrard's injury problems and whether Dietmar Hamann would be fit all the time after the World Cup.
"In fairness to him, he has done well when he has got into the side."
Houllier added: "Regarding Bruno Cheyrou, he is a very skilful, talented player and he came into the team at the right time but he got injured and it took six weeks to come back.
"But once he did recover and returned to the squad, he showed the quality. Once he understands the physical side of the game here, with the skill he has, he will be a tremendous asset for next season."