Spagnuolo will make the decision on which quarterback to start for the rest of the season, Mara said.

McAdoo, who had a 13-15 record with the Giants, had always been a risky choice, since he had no head coaching experience at any level. But in two years as the offensive coordinator under Giants Coach Tom Coughlin, McAdoo, 40, had elevated a moribund Giants attack. When Coughlin was fired after the 2015 season, Manning had personally lobbied Giants ownership on behalf of McAdoo’s candidacy for the head coaching job.

The Giants were impressed with McAdoo’s organizational skills, work ethic, almost fanatical attention to detail and seasoned football acumen. After the Giants bolstered their defense with a free agent spending spree, the Giants surprisingly qualified for the playoffs in McAdoo’s first season. They lost a first-round playoff game to the Green Bay Packers.

But from the beginning, McAdoo seemed an ill fit for the public aspects of his job. He was stiff, humorless and obsessively guarded at news conferences. His communication skills — with the news media and eventually with many of his players — never developed into a strength. Increasingly this season, it appeared that McAdoo had lost the ear, or respect, of many of his players.

Two cornerbacks, Dominique Rodgers-Cromartie and Janoris Jenkins, were suspended after violating basic team rules, like showing up for practice on time.

Then, last week, McAdoo announced that Manning, the team’s revered, two-time Super Bowl-winning quarterback who had started a mind-boggling 210 straight games, would no longer be the team’s starter. Columnists and talk radio callers blasted the move and how it was handled, saying Manning had earned the right to finish out the season at least. Manning was near tears discussing his benching.

Equally galling to Big Blue faithful was that Manning’s replacement was not a heralded rookie who might bring hope for the future, but the journeyman Geno Smith, who had washed out as a starter with, of all teams, the Jets. Smith was a competent 21-for-34 for 212 yards in his debut as starter Sunday.