Giants quarterbacks Daniel Jones, left, and Eli Manning warm up before...

Giants quarterbacks Daniel Jones, left, and Eli Manning warm up before a game against the Cowboys at MetLife Stadium on Nov. 4. Credit: AP/Adam Hunger

In one of Darius Slayton’s first practices with the Giants in the spring, the rookie receiver found himself with a surprising first-team rep.

“We had a pass play and there was a good chance I was going to get targeted,” Slayton told Newsday of that memory. “That was the first time I ever really felt nervous in a practice.”

It wasn’t because of the heightened stage or the desire to impress his new teammates. It was because of the quarterback. Slayton knew he was about to get his first pass from Eli Manning. The 16-year veteran. The two-time Super Bowl MVP.

“All I was thinking was: ‘I can’t drop this ball,’ ” Slayton said.

He caught it.

In Slayton’s 10 regular-season games this season, he hasn’t had to think much about Manning, though. Slayton missed the first two games with a hamstring injury, and since then, his playing career has run parallel to that of Daniel Jones. The two rookies have developed together, building chemistry and trust, while Manning was running the scout teams in practices.

On Monday night, though, Jones will miss a start for the first time because of injury — he’s sidelined by a moderate high ankle sprain — and Slayton will be matched up with Manning again.

He’ll finally get a chance to play in a game with a quarterback he grew up watching win championships, and it’s something he said he will relish. But it’s also an odd dynamic for him and the Giants to have Manning replace Jones at this point in the season. Most teams that lose their starting quarterback to injury have to turn to someone far less experienced with far fewer credentials.

The Giants?

“It’s a next-man-up mentality,” Sterling Shepard said, quickly noting that in this case, the next man is “gonna get a yellow jacket.”

Just when Manning watching and Jones playing had become the new normal for the Giants, the quarterback equilibrium will be upended again. This time it will happen with an eight-game losing streak that is in danger of matching the longest in franchise history, against a division rival that has lost only one game to the Giants in the past five seasons, and it will take place in front of a national Monday Night Football audience.

The biggest difference for the Giants might not be in the quarterback but the quarterback’s legacy. Tight end Evan Engram said the worst part about sitting out this game with the foot sprain that has sidelined him for nearly a month is the missed opportunity for what could be among his last chances to play with Manning. “Personally, that’s what hurts the most,” he said.

It also leads to some unique (i.e. strange) situations. For instance: What do we call Manning? He’s starting this game, but he’s not the team’s starting quarterback. He’s still the backup who just happens to be playing. But he’s also Eli Manning.

Over the past few months, Manning, voted a captain by the team and wearing the C patch on his chest, has not gone to midfield for any pregame coin tosses with his fellow captains. What will he do on Monday night?

And what will happen to the offense?

There are certain things that Jones was able to do physically that Manning simply cannot, just as there are things Manning brings to the field that Jones does not yet have at his disposal.

“There will be a play or two different, but again, Eli’s been ready to go in case he had to play the last 10 weeks,” Pat Shurmur said. “Now he’ll get himself more ready to go.”

As for the on-field mechanics of the passing game, wide receivers coach Tyke Tolbert said his guys don’t concern themselves with who is at quarterback. “Our job is to go out there, line up and make plays in the run game and the pass game,” he said. “Whoever is back there is going to throw and we’re going to catch it.”

Slayton said there wasn’t much difference between catching passes from Jones or Manning in practice this past week.

“It was almost like no change,” he said. “Every quarterback throws a little differently, but they both throw a nice spiral. Obviously, Dan is 16 years younger, so maybe a little more heat on his balls sometimes. But Eli still throws with great pace and great accuracy.”

A pass from Manning at this point does carry more weight (perceived, at least) than one from Jones. Three probable starting skill players — Slayton and Golden Tate at receiver, Kaden Smith at tight end — have never caught one before.

“I’m excited about getting an opportunity to go out and play with him,” Tate said. “We’ll see what happens on Monday.”

And for Slayton? He’s grown a bit and experienced a lot since the spring. That awe factor of being teammates with Manning has worn off a bit.

“Now that I’ve been around here for a while and gotten to know him, he’s a good guy, a cool guy,” he said. “Definitely none of that going into the game.”

After the game, though, it might be a different story.

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