A spokesman for NBC Sports confirmed that Mr. Costas had been told he had "crossed the line," but said it was not because he had discussed the issue of brain injuries and football. Instead, the spokesman said, it was because Mr. Costas had agreed after the symposium at the University of Maryland that he would no longer discuss the issue in interviews without the prior approval of NBC Sports.
He had not sought approval for the CNN interview, spokesman Greg Hughes said Monday.
Shortly after the appearance on CNN, Mr. Costas said, he was told he would not be part of the NBC Super Bowl LII coverage in February 2018. It was a sudden break between NBC and Mr. Costas, his former host of the Olympic Games and "Football Night in America" on NFL Sunday, highly qualified network pre-game show. Last year, he described the separation in public as "mutually acceptable."
The farewell was the culmination of Mr. Costas' faltering commitment for many years to cover the N.F.L. He walked away from NBC coverage in the 1990s, and then said the decision was because "he had ambivalent feelings about football." However, he was anchor of HBO's "Inside the NFL" in the 2000s and then joined NBC's sports coverage in the 2006-7 season, when the network began a $ 600 million deal a year with the league for the games on Sunday night. He continued to present that program, "Sunday Night Football," over the next decade, as awareness of the long-term effects of head injuries increased.
During that time, Mr. Costas used the platform of the highest-rated program to provide comments on everything from weapons to politics. In a part-time commentary in 2012, Mr. Costas called for "enlightened legislation and controls" on firearms one day after a Kansas City Chiefs player shot and killed his girlfriend and then himself.
The network never received criticism or complaints from the N.F.L. about the coverage or comment of Mr. Costas, including his observations at the 2017 symposium, said Mr. Hughes.
By the time Mr. Costas appeared at that event, he had already taken a backseat in NBC coverage. He presented the first "Soccer Night in America" of the 2017-18 football season, but then handed the remaining shows to Mike Tirico, who had moved from ESPN to become the face of the sport's most important sporting events. NBC When NBC finally announced that Mr. Costas would not participate in the Super Bowl broadcast, he said it would not have been fair to those who had been there all season.
"It would not be right for me to parachute and make the Super Bowl," he told The Associated Press weeks before the event. NBC and Mr. Costas officially split up last fall, when they agreed to terminate their contract early.