The brewers have been title sponsors of the tournament, and its second tier competition, the European Shield, for the last four years, spending over pounds 10m in the game. But Jeremy Wilton, head of sponsorship for Heineken's British partner Whitbread, blamed their withdrawal on the inability of competition organisers European Rugby Cup to prevent the English clubs' boycott.
"ERC has been unable to secure the participation of the top English clubs, the two top Welsh clubs, and a UK broadcaster, which we believe devalues the competition," he said.
"Despite these factors we offered a substantial increase in monies to ERC to continue our sponsorship well into the next millennium in order to help develop the competition and to support the secondary European Shield event and to establish a stable environment at the top level for European club rugby.
"Ultimately we were unable to obtain sufficient guarantees from the organisers to secure our continued investment in this event.
"Top level rugby in Europe is exactly where Heineken wishes to be and I hope that we can become involved again in the future.
In this season's competition, the Pontypridd captain, Neil Jenkins, accused his players of making unacceptable errors after a second successive European Cup defeat hit their quarter-final hopes. Colomiers' 35-21 victory in France took them top of Pool D as Pontypridd conceded 17 early points.
"We gave away too many points from our own errors, which is not acceptable at this standard," said Jenkins, whose team will be without injured Wales full-back Kevin Morgan for vital remaining matches against Treviso and Glasgow.