John Elderfield, former chief curator of painting and sculpture at the Museum of Modern Art, remembers the days when scholars spoke freely about whether a particular work was genuine.

They were connoisseurs, this was their field of expertise, and a curator like Kirk Varnedoe, Mr. Elderfield’s predecessor at the Modern, would think nothing of offering his view of a drawing attributed to Rodin, his specialty.

“He was qualified to do it and felt he had a moral obligation to do it,” Mr. Elderfield said.

But when the owner of a painting attributed to Henri Matisse recently asked Mr. Elderfield for his opinion, he demurred. He worried he could be sued if he said the painting was not a real Matisse.

Mr. Elderfield is hardly alone in feeling that art’s celebrated freedom of expression no longer extends to expert opinions on authenticity. As spectacular sums flow through the art market and an expert verdict can make or destroy a fortune, several high-profile legal cases have pushed scholars to censor themselves for fear of becoming entangled in lawsuits.