Leonard, 30, who returned early from the Lions tour to South Africa because of a leg injury that caused him to miss England's defeat in Australia, has written to Quins asking for the release and a counter offer has been made to the club.
Andy Keast, the Quins' new director of rugby who was part of the victorious Lions coaching staff, will not be letting go of England's most-capped prop in a hurry. "There are two years of the contract still to run and we are not prepared to release him," he said.
"We want Jason to stay at the club because he is an important part of our future, but he says he has been made an offer he cannot refuse."
Cardiff are to play Toulouse, the team which defeated them in the inaugural Heineken Cup final two years ago, in a specially arranged match in Toulouse on Sunday. They will also play Nantes a week today on a pre-season tour which their chief executive, Gareth Davies, describes as "a valuable exercise for our players before the season starts".
They return to France to play Brive, this year's Heineken Cup winners, on 9 August to mark the opening of the club's new stadium.
Cardiff are still unaware of their official playing plans for the season after their High Court action against the Welsh Rugby Union, scheduled for yesterday, was postponed until tomorrow.Reuse content