The NFL concussion crisis has hit the league’s helmet makers where it hurts: in the wallet. Riddell, a leading manufacturer of football helmets for the past 85 years, has been struggling without success to sell itself in recent months despite its market dominance, sources told The Post. Ditto for No. 2 Schutt Sports, which recently canceled an auction of the company that makes helmets for NFL stars like Cam Newton and Julio Jones. One big obstacle is Leonard Marshall, the former New York Giants great who is leading a class-action suit on behalf of 4,500 former NFL players against Riddell, alleging the company until 2002 had not properly informed players about the risks of concussions despite knowing better. The legendary lineman says he got a call in July from possible suitors, who offered him cash and an equity stake in the company in exchange for dropping his suit. “I’ve spoken to people interested in purchasing Riddell and they have asked me to set aside my claim,” Marshall told The Post. “I am not going to drop my lawsuit because I am part of a much bigger picture,” said Marshall, who is most famous for his brutal 1991 hit that knocked Joe Montana out of the 1991 NFC championship game. “I feel like there are too many bodies in this for me to withdraw and relieve them of liability,” he said. Marshall’s lawyer Jason Luckasevic, originator of the NFL concussion lawsuit, declined to name the prospective bidder for Riddell, although he revealed it was a firm that primarily manufactures equipment for other sports. Luckasevic said he isn’t worried that BRG Sports, the privately owned parent company of Riddell, will go bankrupt if his clients win their suit. “Riddell has insurance that should cover litigation,” even if it ends up being $500 million, he said.