In the NFL preseason, what you don’t see often is as significant as what you do see.

First-year Eagles coach Nick Sirianni has said on a number of occasions since the start of training camp that his running backs are going to be a big part of the passing game.

“This is no secret,” he said earlier this week. “We really are going to use our running backs in the pass game. We’re going to. They create great mismatches in games.”

But in their first two preseason games, including Thursday night’s ugly 35-0 loss to the New England Patriots at the Linc, the team’s running backs haven’t had much of a role in the passing game. Then again, no position has.

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As a unit, the running backs have nine receptions for 53 yards. Fifth-round Kenny Gainwell has five of those nine catches for 39 yards.

Other than that 79-yard Joe Flacco-to-Quez Watkins screen for a touchdown against the Steelers last week, the Eagles’ passing game has been mostly a rumor.

With Jalen Hurts sitting out Thursday’s game with a stomach disorder, and the Eagles’ three Pro Bowl offensive linemen — center Jason Kelce, right guard Brandon Brooks and right tackle Lane Johnson — all getting the night off, Flacco and No. 3 quarterback Nick Mullens combined for just 110 passing yards, no touchdowns and two interceptions.

Through two games, the Eagles have a 47.2 passer rating and have averaged just 6.2 yards per attempt.

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The Eagles, like most NFL teams, are keeping their cards close to their vest in the preseason. Their offense is very vanilla. Most of the good stuff in their playbook is staying in the playbook until Week 1. What you’ve seen the last two weeks from the Eagles against the Steelers and the Patriots isn’t necessarily what you’re going to get on Sept. 12 when they face the Atlanta Falcons in their season opener. At least you hope not.

Sirianni never has been a head coach before. So opposing defensive coordinators aren’t really sure what his plan of attack is going to be. He likes having that element of surprise right now.

“One of our biggest advantages is that people don’t know exactly what we’re going to do,” Sirianni said after Thursday’s loss.

The Eagles have the weapons to give defenses a lot of different looks. They have enough depth at wide receiver to play 11-personnel (one running back, one tight end, and three wide receivers).

If Zach Ertz doesn’t end up getting traded, Sirianni will have a lethal 12-personnel grouping with him and Dallas Goedert at tight end.

And with versatile running backs like Gainwell and Miles Sanders, Sirianni also can play a lot of two-back 21-personnel.

He used it Thursday on the Eagles’ second offensive play of the game, putting Gainwell and Sanders together in the backfield. Flacco hit Gainwell for a 12-yard completion one play after Sanders ran for 10 yards. Those two plays pretty much were the highlight of the night for the offense.

“We look at all of our personnel groupings,” Sirianni said. “We definitely want to be in 11,” with rookie DeVonta Smith, 2020 first-round pick Jalen Reagor and the speedster Watkins. “We want to be in 12,” with Ertz and Goedert. “And we want to be in 13 [three tight ends] and 21.

“The more things you can do, the more times you can run your base plays out of different personnel sets, the harder you are on a defense. But you don’t want to do those things unless you have the guys able to do them.

“All of those personnel sets I just mentioned, we’ve got players in those roles that we think we can use in those groupings.”

Sanders was held out of the Pittsburgh game last week and played only four snaps against the Patriots, rushing for 13 yards on two carries. With the Eagles holding joint practices against the Jets next week just like they did this week with New England, there’s a good possibility Sanders and many of the team’s other starters won’t play in the preseason finale at the Jets next Friday. The top priority for Sirianni is getting his best players to the season-opening starting line in one piece.

“We wanted to make sure he got a couple of carries in the preseason,” Sirianni said. “With how he felt last week vs. this week, it was our decision as a team not to play him last week. but tonight, we felt he needed to get a couple of carries. And he looked good on those couple of carries.”

Sanders is a dangerous pass-catching weapon. He had 50 receptions on 63 targets as a rookie two years ago and averaged 10.2 yards per catch. He had five catches of 30 yards or more. That was the second most in the league among running backs that year.

In his one full season as a gadget running back in Mike Norvell’s RPO spread offense at the University of Memphis, Gainwell caught 51 passes for 610 yards and three touchdowns on top of 1,459 rushing yards and 13 rushing touchdowns.

Gainwell opted out last year and didn’t play because of the COVID-19 pandemic, which likely is why he fell to the fifth round. But he’s a strong, explosive runner with outstanding pass-catching skills, including exceptional hands and top-notch ball-adjustment ability.

“Kenny had a chip on a defensive end in the Pittsburgh game,” Sirianni said. “As we watched it in the coaches’ meeting, the other guys were like, ‘Oh, that one hurt. That slowed that guy down the next time [he rushed].’

“It was good to see that kind of physical play from him. Kenny also slipped a tackle in that game. The guy had him wrapped up. You just saw how strong he is in the lower body.”

“This kid can do it all,” NFL Network analyst and former NFL offensive lineman Brian Baldinger said of Gainwell in May after the Eagles drafted him. “I don’t know if he’s Charlie Garner, if he’s Brian Westbrook. But he’s like that. He’s a powerful kid.”

Sirianni has moved Gainwell all around the formation. He has lined him up in the backfield, in the slot and out wide. He has put him in motion, both on jet sweeps and as an end-around misdirection weapon.

That’s essentially the same way he was used by Norvell at Memphis, where they played a ton of five-wide-receiver sets.