The veteran lawyer who has guided companies such as Johnson & Johnson and Merck & Co.in their fights against multibillion-dollar product-liability lawsuits was tapped to advise Bayer executives how to up the company’s game against allegations that Roundup causes cancer.

Leverkusen, Germany-based Bayer faces claims by more than 13,000 consumers who blame its glyphosate-based herbicide for their cancers and an estimated cost of as much as $10 billion to settle the litigation. Beisner may be able to offer new approaches for getting juries receptive to arguments the weed killer is safe, said Jean Eggen, a Widener University law professor.

“This guy is known as a fighter, so I don’t think they brought him in to start settling these cases,’’ said Eggen, who teaches classes about environmental law and mass torts — personal injury litigation against corporations that involves large volumes of claims. “Bayer really believes they are right when they say Roundup doesn’t cause cancer.’’