In their quest to build a huge new cultural pier on the West Side of Manhattan, the Hudson River Park Trust and Barry Diller, the media mogul who is paying for it, have faced one seemingly intractable opponent: the City Club of New York, a little-known civic group founded in 1892 that was all but dead a few years ago. But it has gone back to court repeatedly in the last year to stop the project.

The sides are due back in court on Tuesday, when the State Supreme Court’s Appellate Division will hear arguments on whether to dismiss objections to the project or impose an injunction barring further work on it.

But Mr. Diller now says there is a hidden hand at work in all of this, one nursing a grudge and possessing deep pockets. If true, this legal battle could actually be something much bigger — a proxy war between two titans of industry.

“The backer of all this,” Mr. Diller said in a recent interview, “is one Douglas Durst.”

Mr. Durst, the real estate tycoon whose family owns a dozen Manhattan skyscrapers and who was an active supporter of the nonprofit Friends of Hudson River Park, the fund-raising partner of the trust, when it formed in 1999, might seem an unlikely antagonist. He served as chairman of the group and donated $1 million to it.