Foreign satellite cards "threaten the lifeblood of English football" according to the Premier League (PL).
The claim came at a landmark legal battle between the PL and satellite suppliers QC Leisure and AV Station.
PL solicitor Oliver Weingarten told the court that foreign satellite suppliers had hit the Premier League hard.
"The Premier League has suffered significant losses as a result of the defendants' actions, and will continue to do so if the defendants' actions remain unchecked," he said.
"In particular, the sale of non UK Cards in substantial numbers to publicans across the United Kingdom means that fewer legitimate cards are sold to publicans by the Premier League's authorised licensees.
"This has the effect of diluting the value of the Premier League's audio-visual rights as the Premier League's authorised licensees no longer have the benefit of the exclusive right to broadcast particular matches in the United Kingdom."
He added: "Ultimately the quality of English football will suffer."
In his written statement to the court, Weingarten said that at the time proceedings were issued, QC Leisure was advertising Premier League games for as little as £12 a month on its website.
Its website also advertised a "Publican Legal Defence Scheme" for protection in civil and criminal prosecutions.
Weingarten said that while the website denied that QC Leisure's activities were illegal, it also encouraged licensees to continue showing broadcasts of Premier League matches even in the event that it was found to be illegal.
"The section of the website dealing with 'The Law' states : 'What bearing would a potential copyright conviction have on anything other than a fine? Pubs would think, well my Sky bill is over £20k a year, I can get a system for £1,000 if I get caught, I get fined a couple of grand and that's it, even still we feel that it would be immensely difficult to attain a conviction based on the evidence before us."
The hearing continues.