Pressure from the National Football League led to ESPN’s decision on Thursday to pull out of an investigative project with “Frontline” regarding head injuries in the N.F.L. according to two people with direct knowledge of the situation.

ESPN which is owned by the Walt Disney Company pays the N.F.L. more than $1 billion a year to broadcast “Monday Night Football” a ratings juggernaut and cherished source of revenue for Disney.

“Frontline” the PBS public affairs series and ESPN had been working for 15 months on a two-part documentary to be televised in October. But ESPN’s role came under intense pressure by the league the two people said after a trailer for the documentary was released Aug. 6 the day that the project was discussed at a Television Critics Association event in Beverly Hills Calif.

Last week several high-ranking officials convened a lunch meeting at Patroon near the league’s Midtown Manhattan headquarters according to the two people who requested anonymity because they were prohibited by their superiors from discussing the matter publicly. It was a table for four: Roger Goodell commissioner of the N.F.L.; Steve Bornstein president of the NFL Network; ESPN’s president John Skipper; and John Wildhack ESPN’s executive vice president for production.

At the combative meeting the people said league officials conveyed their displeasure with the direction of the documentary which is expected to describe a narrative that has been captured in various news reports over the past decade: the league turning a blind eye to evidence that players were sustaining brain trauma on the field that could lead to profound long-term cognitive disability.

Greg Aiello a spokesman for the N.F.L. said Friday morning that the lunch meeting was requested by ESPN several weeks ago. “At no time did we formally or informally ask them to divorce themselves from the project” Aiello said. “We know the movie was happening and the book was happening and we respond to them as best we can. We deny that we pressured them.”