The big thing was not having a purpose and a place to go every morning. That was the most difficult adjustment for Tom Coughlin.

“The only thing he’s been out of sorts with is his schedule,’’ Sandy Montag, Coughlin’s agent, told The Post on Monday. “He’s a creature of habit. Whether he used to wake up at 4:45 and have his first workout at 5:30, he was a creature of habit and schedule, and now that he didn’t have that he was out of his routine.’’

Coughlin is back in a routine — no, not the routine of coaching, as after 12 years the Giants parted ways with him following the 2015 season. He is now working for the NFL, as he has been named senior advisor to football operations. His first day on the job was Monday.

“We are incredibly pleased to add someone of coach Coughlin’s experience and character to our staff,” NFL Commissioner Roger Goodell said in a statement. “His passion for football is evident and we are confident he will contribute a great deal to the betterment of the game for current and future players as well as for fans at every level of our sport.”

Coughlin will work closely with Troy Vincent, the NFL’s executive vice president of football operations, on what the league says is a variety of issues to support and improve the game. Coughlin will advise game-related league committees and “provide strategic guidance on other matters, including playing rules, coaching techniques and the development of football personnel.’’ He also will provide input to the operation of the NFL draft and Pro Bowl.

“I am looking forward to working with Commissioner Goodell and the talented people representing the National Football League,” Coughlin said in a release. “My purpose is to serve for the betterment of the great game of football.”

Coughlin, who turns 70 on Aug. 31, will not have any dealings with officiating issues or player discipline. He will travel to NFL training camps and may travel to games.

“This role in the NFL doesn’t really exist right now,’’ Montag said. “It did in the past, I think [former Giants general manager] George Young had the first role like this, Ernie [Accorsi] had it, Art Shell may have had it. It is really looking after the game of football itself. There’s really no better person to do that than Tom.

“It’s almost like he’s a head coach now and he’s responsible for improving everyone’s game, if you will. He’s really excited about it. He wanted to stay involved in some regard, this made the most sense.’’

Coughlin is also highly involved with his Jay Fund, which supports families of children dealing with cancer. Montag stressed that this newly created NFL position is a full-time job and that “Tom’s not going to do something that’s ceremonial. He wants to make sure he can have an impact on making the NFL even better than it is, specifically the level of play.’’

The Giants decided to make a change after last season’s 6-10 record — the third consecutive losing season under Coughlin. After flirting with the idea of coaching again — he spoke with the Eagles and 49ers — Coughlin looked elsewhere, and this NFL opportunity arose.

“Representing coaches my whole life, including my first client, John Madden, I know this, coaches never get the bug out of them,’’ Montag said. “There’s always one small itch somewhere for every coach. What I know is Tom is happy, this is a great role for him. He’s just looking forward to having an impact on the game.’’