It’s been a miserable season for Eli Manning and the Giants. (Al Bello/Getty Images)

The beginning of the end clearly has arrived for quarterback Eli Manning with the New York Giants.

What is not as clear, however, is exactly how long it will take for that ending to play out and exactly what it will look like.

“The Giants under Eli won two Super Bowls because of the way Eli played during the playoffs,” former Washington Redskins quarterback Joe Theismann said. “Those were teams that were not dominant teams, by any stretch. He deserves all the credit in the world for those two Super Bowls. But this has been going on for a while. It doesn’t just start in one year. I do think we’re seeing the end for him in New York with the Giants. I really do.”

To Theismann and some other observers, it’s time for the Giants to find Manning’s successor and move on. The Giants, after reaching the playoffs last season in Coach Ben McAdoo’s rookie season, are 1-7. Manning, playing behind a shaky offensive line and without injured wide receivers Odell Beckham Jr. and Brandon Marshall, has struggled. He is 36 and, at times, has looked older.

“The pieces around him aren’t very good,” Theismann said in a phone interview. “They aren’t what they were. This is a team that looked at five guys on the offensive line who struggled last year and decided not to do anything about it. So the offensive line isn’t very good. The wide receivers are completely depleted. The defense hasn’t stepped up to the level of last year.

“But he can’t get out of the way very well. It seems like he’s even more immobile than Tom [Brady] is. And if you watch Eli play, he’s going to throw two passes a game right to the other team. The only question is whether they catch them or not. Is it Eli? No. He has no supporting cast and the parts around him aren’t getting better. But it is time for them to start looking.”

The Giants opted not to deal Manning to the Jacksonville Jaguars or anyone else by last week’s NFL trade deadline. The Jaguars have Tom Coughlin — Manning’s coach when the Giants won Super Bowls in the 2007 and 2011 seasons by beating Brady and the New England Patriots — running their football operations. They have a young and dominant defense but a still-unreliable quarterback in Blake Bortles. A deal might have made sense, assuming that Coughlin believes that adding Manning would represent an upgrade at quarterback.

“The question going forward is whether Tom Coughlin is going to step in and want him,” Theismann said. “It can’t happen this season because of the trade deadline. But Jacksonville is going to have to do something. They’re going to have to find an answer. If I were them, I’d enter the Kirk Cousins sweepstakes.”

With Manning staying put at least for now, he and the Giants have reached the playing-out-the-string portion of a miserable season. Co-owners John Mara and Steve Tisch are known for patience — perhaps not Pittsburgh Steelers-level patience with coaches, but patience nonetheless. Even so, that patience surely is being tested and the rest of this season could be about the futures of Manning, McAdoo and General Manager Jerry Reese with the organization.

McAdoo stuck with Manning as the starter this week after briefly mentioning the possibility of being open to changes at all positions, including quarterback. Manning is to start Sunday’s game at San Francisco against the winless 49ers, just as he has started every Giants’ game since taking over for Kurt Warner during his rookie season in 2004.

“My goal is to prepare every week and do my job…. He [McAdoo] said he’s got faith in me and keep grinding,” Manning said during his weekly media session. “So that’s what we’re doing…. I’m happy to be out there each and every week with my teammates. That’s a goal of mine to stay healthy, to play through injuries, to be accountable. That is important to me to be there for my team and my teammates. But it’s not about breaking a record, though.”

Manning is well-versed in the ways of the NFL. His father Archie played in the league and, along with agent Tom Condon, helped Eli to orchestrate the draft-day trade that kept Eli out of San Diego. Older brother Peyton didn’t get to finish his NFL career in Indianapolis, but moved on to Denver and managed his second career Super Bowl triumph with the Broncos.

Still, if the Giants are going to move on, they will have to shove Manning aside. Nudging him gently is unlikely to get it done.

“I want to play,” Manning said. “That’s what I like to do. I like to play football and play quarterback. I understand that I’ve got a job to do and I’ve got to do it better and do it well and get wins. And if you don’t, everybody’s job is up for grabs in this league.”

Manning’s backup is Geno Smith. The Giants also have rookie Davis Webb, a third-round draft choice in April out of Cal, on the roster.

They could end up with one of the first few picks in next year’s NFL draft. The 2018 quarterback draft class includes well-regarded prospects such as Sam Darnold of USC, Josh Rosen of UCLA and Josh Allen of Wyoming.

“The guys they have aren’t the answer,” Theismann said. “It’s certainly time for the Giants to start looking. In Arizona, it’s time for them to start looking. In New England, Tom doesn’t fit any mold. He might go on forever. But other teams don’t have that luxury. I do think we’re seeing the end.”

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