The search engine, which purchased YouTube in October 2006, made the comment in a highly confidential document, which was obtained by Viacom and presented in the company's lawsuit against Google.
Viacom sued Google in 2007 for $1bn in damages for hosting infringing content on YouTube.
The comments came to light after the latest batch of documents used in the case, which is expected to go to trial later this year, were unsealed.
According to the Associated Press, in other unsealed case documents Google labelled YouTube as a "rogue enabler of content theft".
The search engine also proposed it distance itself from the video-sharing site "based on our respect for copyright" and that a "play first, deal later" policy should be adopted when dealing with "hot content".
"It's revealing that Viacom is trying to litigate this case in the press," YouTube said.
"These documents aren't new. They are taken out of context and have nothing to do with this lawsuit."
The move comes just a month after YouTube claimed Viacom had been "continuously and secretly" uploading its own content to the video-sharing site for years.
See also: YouTube suffers outage
This story, "Google: YouTube was sustained by piracy" was originally published by Macworld U.K..