"I am contracted to Harlequins until the end of the 2013/14 season," said O'Shea. "I will be honouring that commitment and, hopefully, continuing beyond it."
And he believes the quarter-final could prove a memorable contest and occasion.
"Sunday will be an unbelievably exciting day to be a Harlequins supporter, with the club playing in a home quarter-final for only the second time in its history," he said.
"It will be the team that has come a long way against the team that has arguably made the Heineken Cup what it is today.
"We are looking forward to what will be an amazing occasion at The Stoop. The two teams will be incredibly well-supported and it's going to be a great day."
And Harlequins captain Chris Robshaw added: "As a player you want to test yourself against the best and the knock-out stages of the Heineken Cup certainly provide an opportunity to do so.
"And when it comes to a test, they don't come much tougher than Munster. We're looking forward to a great match and a great occasion at The Stoop on Sunday."