Dunne and Collins are understood to have been fined two weeks' wages by Villa after being involved in a row with coaching staff during a team bonding session last week.
Yet Houllier said: "Richard Dunne and James Collins have been disciplined and this is all I will be saying on the matter.
"As far as we are concerned, this is the end of the matter.
"The club have dealt with the incident strongly and quickly, but now we move onto the main target which is the Wolverhampton game.
"It was difficult for me to be involved in the investigation and give any kind of punishment.
"I did not want to be involved because I think it was better not to be pre-judging. I prefer to have neutral people."
Source: PA
Source: PA